As I've observed the workings of Protestantism over the years, both as an insider and an outsider, one of the things I've noticed is that when Protestantism goes wrong (from a Catholic point of view), it often does so by means of what might be called "hyper-pietistic exaggeration." What I mean is this: Various forms or expressions of Protestantism will often latch onto some true doctrine of the Catholic faith, being extremely zealous for that doctrine, and in their zeal they exaggerate that doctrine to the point that the doctrine ends up self-destructing. Along the way, false dichotomies are often created which pit the true doctrine latched upon against other true doctrines, creating competition where there should rather be complementarity. The Catholic response, then, is to recognize the good being defended, but to try to help restore some balance.
I will provide a few examples below to illustrate this phenomenon. However, I would also note that, of course, not all Protestants share all or any of these errors. I think these are tendencies within certain mainstream Protestant circles, but they are certainly not universal. Also, in some cases I think it is possible to construe Protestant teaching in ways that avoid these errors. Sometimes Catholics have too harshly judged certain expressions of Protestantism, not allowing for better interpretations. This is the case in particular, I think, when it comes to classic Protestant formulations of predestination and free will and justification, as I mention below. Nevertheless, I think the "hyper-pietistic" tendency is alive and well in much of Protestantism and helps account for many theological conflicts between Catholics and Protestants.
Whereas Pelagianism and its mitigated sister heresy Semipelagiansim deny the necessity or the sufficiency of the grace of God for our salvation, Protestantism has often tended rather to emphasize the grace of God in our salvation to the point that this drowns out other important true doctrines. This can be seen in the classic Reformed/Lutheran doctrine of justification.
Catholics hold that no one can be righteous on his own. Since the Fall of Adam, we are all born in a fallen condition in which we are inclined to sin. Left to ourselves, we are doomed. Our only hope is that God sent his Son to die for us, so that his sacrifice and merits might purchase for us forgiveness of sins and the grace necessary to be holy. That grace is applied to us by the Holy Spirit, who changes our inmost being and makes us holy. Thus, we can become righteous before God by a gift of his grace.
A good portion of mainstream Protestantism, however, has issues with this scheme. In their opinion, if we can become truly righteous by grace, this takes away from the glory of God and gives us too much to boast of. What they want to say instead is that our sins are so great that we can never be righteous before God in our personal lives. Rather, what happens in justification is that Christ forgives our sins and credits his own righteousness to us, so that his righteousness counts for ours. We never get to be righteous enough to be acceptable to God, but Christ is righteous for us so that that's OK. The Holy Spirit does sanctify us and change our lives, but this change does not make us any more acceptable to God, because if there is one sin on our record, no internal righteousness matters at all. We are still fit only for hell. So when God looks at us in terms of our personal lives, he sees people who are fit only for hell. But Christ, as it were, stands in front of us, and God sees that Christ is righteous and acceptable, so he accepts us too because of him.
In this Protestant view, what should have been complementary has become contradictory. In Catholicism, through the grace of God we can become truly righteous and pleasing to God. All the glory goes to Christ because it is through the merits of Christ alone that we receive the grace to be righteous. Christ is holy, and therefore, by his gift, we too can be holy. But in the Protestant view, it must be either Christ or us. If Christ is righteous and gets the glory for our salvation, this must imply that we cannot become righteous, for if we could actually become righteous, the glory would proportionably be taken away from Christ. In its zeal to uphold and defend (and rightly so) the graciousness of our salvation, Protestantism has ended up gutting that salvation by taking away from it the ability to truly make us pleasing to God.
To make an analogy: When an artist creates a sculpture, we normally say that the artist's praise increases along with the quality of his art. But the Protestant view is like saying that to the extent that the sculpture becomes beautiful, this takes away praise from the artist; so in order to ensure the praise of the artist, we must maintain that the sculpture is ugly.
2. Grace and free will.
In the Catholic view, grace is the source in us of all our good. But grace does not do away with our free will. It is by grace that we become righteous, but we must voluntarily choose to cooperate with grace. This cooperation itself is a gift of grace, so all is grace, but our free choice is still essential.
Mainstream Protestantism, however, has historically reacted strongly against this view, insisting that if our salvation is owing to the grace of God, there can be no place for the cooperation of free will. Again, what should be complementary is made contradictory and competitive. Instead of the Catholic position of "grace, therefore free will," Protestantism has "grace, therefore no free will."
But by undercutting free will, this Protestant view has undercut the very glory of grace. For it is to the praise of God's grace that it can make the ungodly become godly. Without free will, however, there can be no moral responsibility. There can be no sin or righteousness, because these moral qualities belong to the will. Where there is no will, there is no morality, whether good or bad. So once again, in its zeal to protect the grace of God, Protestantism ends up protecting grace from its own best fruits and therefore ends up trivializing it.
(Now, as I alluded to above, I should say that in these two matters of justification and free will, there are more positive ways of interpreting Protestantism which do not commit it to these absurdities. See here and here, for example. However, many Protestants have indeed held to one or both of these absurdities to one degree or another; and even in cases where the substantial doctrine may be sound, Protestants have maintained arguments with Catholics over the language of Catholic doctrine--such as objecting to the word "cooperation" in connection to free will and grace--and have often created imbalances by means of their own distinctive language.)
3. Sola Scriptura.
The revelation of God is often called in Scripture "the word of God." In the Catholic view, God has given us his word in the Scriptures of the Old and New Testaments. He has also handed down his word through the teaching and practices--that is, through the Tradition--of the Church. He has entrusted the Church with the authoritative teaching of the word of God. So we need all three--the Bible, the Tradition of the Church, and the teaching authority of the Church--in order to rightly understand and apply the word of God.
But instead of seeing these three elements as complementary, Protestantism, since Martin Luther, has pitted the Bible against the other two. The Protestant attitude tends to be that we must choose between the authority of the Bible and the authority of the Church. In its zeal to defend the authority of the Scriptures, Protestantism has rejected the authority of the Church and its Tradition. In this view, if we appeal to the authority of the Church or its Tradition, we must be denigrating the Scriptures and therefore the word of God itself. The historical result of this false dichtomy has been the splitting of the Church as Protestants pitted their own private interpretations of the Bible against the authoritative teachings of the Church handed down through the ages, causing rifts in the unity of the Church that continue to this day. Also, although the goal has been to defend the Bible, the result has been the undermining of biblical authority. Once the Bible has been taken out of its proper context in the Church, it becomes unable to provide what is needed for the maintenence of the people of God. The Bible simply wasn't designed to function without a context of authoritative interpretation. It doesn't answer all the questions that need answering. Therefore, Protestantism's defense of biblical authority has resulted in endless divisions among Protestants as different groups reject the biblical interpretations of others in the name of their own interpretations. Since everything seems to be interpretation, and often very stretched interpretation as different groups and individuals try to make the Bible answer doctrinal questions it simply doesn't answer, people feel free to dissent from everyone else's interpretations and simply go their own way, making the Bible a wax nose to justify whatever theology has been preferred or adopted. In many cases, a kind of relativism has resulted as well, as many people to some degree or another have given up hope that clear, conclusive doctrine can be established in many areas, and they have settled down to accepting multiple contradictory doctrinal opinions with apathy. In fact, I think it is clear that much of the relativism and agnosticism of modern western culture gained ascendency directly as a result of the shattering of Christendom by the Protestant Reformation.
4. The intercession of the saints.
In the Catholic view, God alone is to be worshiped. But God shares his grace with us, lifting us up to share in his divine life. He redeemes us from sin and makes us holy. He adopts us as his beloved children. Because of God's graciousness to us, we humans can be truly pleasing to God, and God hears our prayers as a Father hears his children. Therefore, part of a proper honoring of God is an honoring of God's work in his redeemed people. We honor the saints--those made holy by God's grace. All of us who have received and followed the grace of God are saints, but some are further along the path to holiness than others. Some--like the apostles, or Mary the mother of Christ, or those who have died and been perfected by grace and are in the presence of God--are particularly close to God. We should pray for each other, and ask each other for prayer. We should especially seek the prayers and intercession of those who are especially close to God. God listens to our prayers and the prayers of others in this world and often does great good in response to them. He also responds to the prayers of those made perfect in heaven, to the prayers of the holy apostles and martyrs, and to the prayers of his blessed mother. God alone is to be worshiped, but we should honor his work in his saints. Christ alone is the true intercessor--in the sense that he alone has merited all the grace that unites us to God--and yet the saints are also intercessors under him, because Christ has honored us by making us co-workers with his grace. There is a complementary relationship here. Christ is God and is the source of all grace, and therefore the saints, through grace, are made holy and praiseworthy and able to intercede for each other under him.
But Protestantism has tended to take this complementarity and turn it into competition. In the classic Protestant view, if we speak to the saints in heaven and ask for their intercession, we are derogating from the glory of Christ as the one mediator between God and man (although, for some reason, this is not held to be the case if we pray for each other here on earth). If we honor Mary the Mother of God and the saints, we are taking away the proper worship due to God. In order to safeguard the worship of God alone and Christ's unique intercessory role, Protestantism abolishes or downplays the glory of God's grace in his redeemed people. Instead of honoring (on a divine level) Christ and therefore honoring (on a creaturely level) the saints, we must honor Christ and therefore not honor the saints. Instead of looking to Christ as our mediator with God and therefore also looking for the intercession of God's people redeemed and empowered by Christ's grace, we must look to Christ as our mediator and therefore avoid looking to God's people as subordinate intercessors. Once again, instead of allowing the stream to be honored by praising how it flows out and gives life to the world, Protestantism tries to honor the stream by stopping up its exits, keeping it underground, and trying very hard to make sure it never gets anything wet.
5. Temptation and sin.
In the Catholic view, Adam's Fall has affected us all, in that we are all born into this world with an inclination to sin which is insurmountable without the grace of God in Christ. This condition is called "original sin." In the state of original sin, we no longer have the grace of God given to Adam and Eve in the Garden of Eden which kept them in a right relationship with God. God's grace enabled their will to be in a right relationship with God, and also enabled their reason to reign over their passions and inclinations. After the Fall, man has been without this help (apart from Christ and his work of redemption, which brings grace to us once again), and so his will has been averse to God and his reason often falls to his passions. We are subject to all sorts of disorders which make it difficult for us to be holy and which draw us into sin. But Catholicism distinguishes between our corrupted condition which makes us prone to sin and sin itself. Our fallen condition makes us susceptible to various temptations and inclines us to sin, but personal sin, properly speaking, only occurs if our will consents to the temptation. If, by grace, we resist these temptations, we may still be subject to our fallen corruption, but we are not committing personal sin.
We might illustrate this by referring to same-sex attraction. In an unfallen condition, people would presumably not be subject to the disorder of same-sex attraction. In our fallen condition, however, it seems that some people are subject to this. Our passions have become corrupted such that we are often inclined towards that which is wrong or harmful in all kinds of ways. However, in the Catholic view, merely having a disordered inclination to same-sex attraction is not itself a personal sin on the part of the person attracted. If the person resists the temptation and fights against it, choosing to pursue holiness, the temptation can actually become an occasion for the development and expression of great virtue. If the person chooses with his will, however, to forsake the good and embrace the disorder, now a personal sin has been committed.
Mainstream historic Protestantism, however, has tended to reject the distinction between disordered inclinations (in theological language, "concupiscence") and personal sin. According to this view, the mere fact of having a disordered inclination constitutes a personal sin. Just in the past couple of days, I had a conversation with a Reformed Protestant about same-sex attraction. He maintained that same-sex attraction is itself a personal sin, and therefore anyone who feels attraction to another person of the same sex is by that fact alone engaged in committing personal sin, even if with his will he rejects and refuses to cooperate with the inclination or the attraction.
This position seems motivated by a zeal to honor God by taking sin seriously and refusing to excuse it or mitigate condemnation of it. But this zeal is taken to such an extreme that it ends up actually undercutting a sense of the seriousness of sin. If all disordered desires are sins, then it becomes very difficult (to understate the case) to maintain a distinction between temptation and sin. Inclinations beyond our control are now labeled "personal sin" and we are told we should feel personally guilty for them. But if I can't do anything about committing sin (because at least some sin is no longer fundamentally voluntary), then I cease to be motivated to do anything about it. Lack of belief in the possibility of overcoming something naturally leads to apathy about attempting to overcome it. So the natural end result of this is a kind of apathy towards sin and an excusing of it. "Oh look, I sinned again! Well, I do this all the time anyway, and there's nothing I can do about it, so there's no need to worry about it." With this kind of thinking, it is easy for patterns of real sin to become established in a person's life, since it is believed that there is no moral difference between a person who resists temptation and a person who gives in to it, or at least that the moral difference is greatly diminished because both are still guilty.
If I see sin as something I do from time to time but not all the time, and I can pinpoint particular sins that I have committed, and I have a hope of avoiding these sins by the grace of God, then I might be motivated to fight against sin and work to avoid it. But if I see sin as something I am always committing all the time, in every action, and there is nothing I can do about it, then it becomes much easier just to let sin slide as an inevitability not worth bothering about. God will forgive me anyway and let me into heaven whether I stop or not, since otherwise no one could be saved! Especially if we combine this with the doctrine of justification discussed earlier, this way of thinking can be a potent motivation to trivialize sin. Thus, once again, an overzealous but not-well-thought-out attempt to protect a true good ends up undercutting that very good.
(When I was a Protestant, I tended to avoid the kind of thinking I am describing here. I think that one can certainly be a Protestant and avoid it. But many Protestants have fallen into it. Even when I was a Protestant, I felt that a lot of people in my Reformed circles tended to have some distortions in this direction. It is therefore a good example of a common tendency.)
In the Catholic view, God often relates to us through means that unite us to him and to his grace. Certainly the greatest illustration of this is the sacraments. In the sacrament of Confession, for example, we confess our sins to a priest, who exercises authority from Christ to declare his forgiveness of those sins. In the Eucharist, or Communion, the fruits of Christ's sacrifice on the cross are made present to us and Christ himself is made present to us through bread and wine and the partaking of bread and wine. Catholics call the Eucharist itself a sacrifice because in it Christ's one true sacrifice on the cross is offered up to God and its fruits are received by us.
Protestants have historically expressed great concerns over these Catholic ideas. They have rejected the sacrament of Confession altogether, declaring that since God is the one who forgives sins, there can be no need for confession to a priest. With regard to the Eucharist, most of them have kept this sacrament, but some of them have turned it into a mere memorial of Christ's death which does not really and truly make present Christ and the fruits of his sacrifice. Others have kept more of the Catholic idea, but are still greatly uncomfortable when Catholics start talking about how Christ is truly present--body, blood, soul, and divinity--in the sacrament and how the sacrament is a kind of sacrifice in which we truly receive the fruits of Christ's sacrifice and offer that sacrifice up to God. They say that if the Eucharist is a sacrifice, that must mean that Christ's sacrifice on the cross was insufficient.
Again, we see here the Protestant tendency towards false dichotomies resulting from overzealous protection of real truths. There is a desire to protect God's sovereignty as the one who forgives sins, and to protect the status of Christ's sacrifice on the cross as the only sacrifice that takes away our sins. These are good intentions. But confession to a priest is not a replacement of God's role as the forgiver of sins, but rather a means through which God exercises that role. The Protestant view is as if one were to say that if a king sends an ambassador, the very existence of the ambassador takes away from the authority of the king. "So, which will it be?" they ask, "Does the king have authority to give orders, or does the king's ambassador have the authority to deliver the king's orders?" "Well," we reply, "there's no need to make a choice here. The answer is yes. The king has authority to give orders, and he exercises that authority partly in authorizing an ambassador to deliver those orders." Another analogy: If I authorize my 17-year-old daughter to give orders to her younger siblings while babysitting, is this the same as abdicating my own authority as a parent? This seems to be the Protestant way of thinking. If I have to confess my sins to a priest as God's representative, and he has authority to pronounce God's absolution, then this somehow implies that God's role as the forgiver of sins has been usurped.
With regard the Eucharist, the Protestant view seems to be that either Christ's sacrifice on the cross was the one true sacrifice sufficient to take away our sins or the Eucharist is an offering up of that one sacrifice to God and a partaking in its benefits. But why make a competition between the source of our salvation and the application of that source to us? It is like saying that since someone has written me a check, there should be no need for me to cash that check in; and that if I have to cash the check in, that is the same as saying that the check didn't provide for me a sufficient amount of money. This just doesn't make any sense. It is a false dichotomy arising out of a less-than-adequately-thought-out pious zeal.
7. Presuppositional apologetics.
"Presuppositional apologetics," at least under that name, is something that was invented by Cornelius Van Til, a Reformed thinker from the first half of the twentieth century. This narrow school of thought is certainly not representative of the broad spectrum of Protestants. However, the kind of general attitude expressed in many forms of presuppositional apologetics has often been expressed in Protestant thought in various other contexts as well. The presuppositionalist attitude thus provides another good example of the Protestant tendencies we've been discussing.
Presuppositionalists point out that God is the Supreme Being. He is the First Cause, and there is no being behind him, no being from whence he came. One cannot find anything more ultimate than God. God is the source of all reality. God is a necessary being. Therefore, the existence of God is necessary to posit in order to be able to make sense of any other aspect of reality, even the foundations of reality itself down to the basic laws of logic.
All of this is well and good. In fact, I think that presuppositionalists have done a great service by calling attention to these crucially important truths and emphasizing them. But, as with the other examples we've seen, what starts out well ends up going badly as a well-motivated pious zeal becomes unbalanced and ends up creating exaggerations and false dichotomies.
Many presuppositionalists, starting from the propositions mentioned above, argue that it is impermissible to make arguments for the existence of God. We should instead just assume God's existence without argument. To make an argument for God's existence, they reason, one would have to place the reasons of one's argument above God. One would have to start with something before God and derive God from that. But God can't be derived from anything, they say, because he's God! So the very attempt to make an argument or to give a reason for believing in God's existence is in its very nature a betrayal of God. Piety towards God demands that we simply accept him, and that is that.
The problem here is a confusion between ontology and epistemology. In other words, these presuppositionalists are confusing God's status as the Supreme Being with our need to have a reason to believe that the Supreme Being exists. It is as if someone were to argue that if we make any attempt to prove that Queen Elizabeth is the rightful queen of England, we have thereby put ourselves above Queen Elizabeth, giving ourselves a higher place of authority than she. But this is, of course, absurd. If I give reasons to think that Queen Elizabeth is the queen, this is not the same as actually making Queen Elizabeth the queen. To examine the evidence to see if Queen Elizabeth actually has the authority she claims to have is not the same as positing some authority higher than Queen Elizabeth which gives her her authority. Similarly, examining evidence to see if there really is a Supreme Being is not the same as positing the existence of something above the Supreme Being which gives existence to the Supreme Being. If I say, "If X, then God. X, therefore God," I am not saying, "X makes God to be God." X is not usurping God's position. Rather the reverse. If X requires God, that means that X is dependent upon God. I am examining X and determining that X needs God to exist in order for X to exist, and then reasoning that since X exists, God must exist. Rather than undermining God's supremacy, such an argument simply gives me grounds for recognizing the truth of God's supremacy.
Once again, this very Protestant (and particularly Reformed) movement of presuppositional apologetics starts out with a very well-motivated zeal to emphasize the supremacy of God. It rightly points out that God is the supreme and necessary Being and that this has fundamental implications for every aspect of reality. But then it allows that zeal to become unbalanced and to undercut itself. If God's supremacy means that we are not allowed to examine reasons to believe in God's supremacy, then we can never have any reasons to believe in God's supremacy. The result is that we must hold the idea of God's supremacy to be groundless (so far as we can see) and therefore foolish to believe in. So we destroy the idea of God in order to protect the idea of God.
The Catholic view, on the other hand, has a rich tradition of classical apologetics which makes rational arguments to show that God exists (and that he is the Supreme Being), keeping distinct the fact of God's supreme being from how we know that he is.
(I should add that not all forms of presuppositional apologetics make the mistake I discuss here. Some forms of it are more sound than others. But the tendency towards overzealous exaggeration remains.)
In conclusion, I think it is valuable to explore and to articulate the tendencies that seem to lie behind many of these Protestant errors. If we can recognize the causes and the characteristics of erroneous thinking, it makes it harder for that thinking to go undetected and easier for those infected by it to understand alternative points of view. It is also valuable for Catholics to understand the motivations and concerns that lie behind various Protestant objections to Catholic teaching--which, without such understanding, can often seem mystifying--so that they can address those concerns more effectively.
There are a number of links embedded above for further reading. In addition to those, for more on the general Catholic doctrine of salvation, see here. For more on justification, see here and here. For more on grace and free will, see here and here. For more on Sola Scriptura, see here and here. For more on the sacraments, the intercession of the Saints, Mary, and a bunch of other things, see here, here, here, here, and here.