Church Discipline Is, in Theory, Compatible with Sola Scriptura
In their arguments against Sola Scriptura, I have frequently heard Catholics argue that Protestant churches are acting hypocritically when they discipline members for disagreeing with or opposing the teaching of the church, given the teaching of Sola Scriptura. The argument often goes something like this: "Sola Scriptura teaches that there is no Magisterium, no Supreme Court in the Church that determines what the true interpretation of Scripture is. Rather, everyone has a right to interpret Scripture for themselves. This is called the 'right of private judgment'. Each Protestant church can maintain its own existence only by maintaining this right, because their independent position is based on their own unique biblical interpretations. But Protestant churches, particularly confessional churches that have courts that try people for false teaching, are being hypocritical, because the leaders maintain their own positions by means of the right of private judgment, while they deny that right to their members and discipline them for disagreeing with the biblical interpretations of the leaders. They tell everyone to practice Sola Scriptura--which includes the right of private judgment--but then they discipline them when they do so."
I think this argument--or at least this form of it--is fundamentally flawed. Here's why: Protestants who affirm Sola Scriptura do not affirm a "right of private judgment" understood as described above. No such right is inherent in the idea of Sola Scriptura. Protestants (at least historical, theologically-conservative, confessional Protestants) do not teach that people have a right to interpret Scripture any way they like. Protestants affirm rather that the Bible is the supreme authority in matters of doctrine, and that everyone has a duty to agree with the Bible. Confessional Protestant churches affirm the Bible as the supreme authority, so they do indeed recognize a right and a duty belonging to each Christian to check the views of their leaders against the teachings of Scripture and to reject those views if they go against Scripture. But if, instead, it is the leaders' position that is in accord with Scripture, the church member has no right to oppose it but rather a duty to submit to it. So if a church member opposes the teaching of Scripture which is enshrined in the church's official confession, the church has every right to discipline that member. Such discipline is perfectly consistent with the idea of Sola Scriptura.
In short, confessional Protestants do not teach that everyone's individual interpretation of Scripture is the ultimate authority, or that everyone's personal views are the ultimate authority; rather, they teach that Scripture, rightly interpreted is the ultimate authority, and everyone has a duty to conform their views to Scripture. So it is perfectly appropriate, then, for churches to discipline members for rejecting or opposing the proper interpretation of Scripture on the basis of their own false interpretations of Scripture.
Church Discipline Is, in Practice, Often Incompatible to Some Degree with Sola Scriptura
However, while this common Catholic argument is fundamentally flawed in the way it is often formulated, there is some truth to it. Sola Scriptura does say that every individual has the right and the duty to conduct his own investigation into the meaning of Scripture and, after he has done so, to stick with that interpretation even in opposition to church leadership. That investigation must be conducted with care, diligence, humility, and prayer, with deference to the Church's tradition, to the great doctors of the Church, to the work of scholars, etc. It cannot be a sloppy, haphazard, biased investigation. But, once a properly-executed investigation of Scripture is carried out, every individual has a right and a duty to follow the interpretation that emerges from such a study--not because every individual has a right to believe whatever he wants, but because every individual has a duty to follow Scripture as the supreme standard.
However, under the Sola Scriptura view, unlike in Catholicism, there is no human Supreme Court on earth in doctrinal matters that can be looked to with implicit trust to provide the objectively-correct interpretation of Scripture. This causes some serious problems in Protestant practice that Catholics (and others) have often justly pointed out.
1. For one thing, even if Scripture is perfectly plain and clear in its teachings, the lack of a human supreme doctrinal court tends to contribute to a significant amount of anarchy and division among Protestants. It is evident why that would be the case, when we understand human nature. A church may have come to the correct understanding of Scripture, and enshrined that understanding in their confession of faith. A church member comes along and opposes that teaching. The church attempts to discipline that member, but the member says, "I have the right and duty to conduct my own investigation into the meaning of Scripture. I have done so, and I find your interpretation incorrect. So, since Scripture is a higher standard, a higher court of appeal, than you are, and since you disagree with Scripture, I have a right and a duty to refuse to submit to your discipline and to continue to promote what I see Scripture as teaching. We must obey God rather than men." There is no human court to which both sides in this dispute can turn to adjudicate this difference over the proper interpretation of Scripture, so this controversy must end at an impasse, practically speaking, unless one side changes their view. The two sides will go their separate ways, both insisting that they are right because they are in accord with the true supreme standard--the Scriptures.
Here is a statement of this problem coming, not from a Catholic, but from an Atheist Libertarian author:
The likelihood of conflicting interpretations of special revelation did not pose as much of a theoretical problem for Catholics as it did for Protestants. In the Catholic Church the pope was the ultimate arbiter of doctrinal controversies. His function was rather like that of the Supreme Court in American law; what the pope said was final, and that was the end of the matter (at least in theory). But Protestants, in rejecting papal authority and in maintaining that each person should use his or her own conscience to understand Scripture, generated a serious problem for themselves. Hundreds of Protestant sects arose, and their conflicting interpretations of the Bible frequently spilled over into politics. Thus Catholic critics of Luther, Calvin, and other Reformers were basically correct when they predicted that the Protestant approach to the Bible would result in a type of religious anarchy, as each individual viewed himself as the supreme authority in religious matters. Reverting to my previous analogy, the result was similar to what would happen if America had no Supreme Court, or judicial system of any kind, and each American was free to interpret and implement law according to his own judgment.
2. This problem is exacerbated by the fact that, in reality, Scripture is not always completely plain and clear. Certainly, there are some things on which Scripture is so explicit and clear that hardly anyone will be able to find themselves in honest disagreement with what almost everyone can see that it says. For example, if someone wants to argue that Jesus was just an ordinary human being, it is pretty easy to see that Scripture is clearly against such a view.
However, on many issues which often constitute the basis of theological controversy, Scripture is not so explicitly clear. Take infant baptism, for example. This is one of the issues over which Protestants and Protestant churches have often been divided. Scripture never explicitly addresses the subject. And yet this is an issue that cannot be avoided. A church must take some stand on this subject. It must embrace and practice infant baptism, oppose infant baptism, allow infant baptism as optional, etc. Any church cannot but take some position on this issue that others disagree with. Since Scripture never explicitly addresses this subject, nor even clearly and plainly hints at it, if one is practicing Sola Scripture one must come to one's convictions on this subject by looking at what Scripture does say and trying to infer, based on all available evidence, what the most likely correct answer is. But here we are into complex literary and doctrinal interpretation, and at this level of interpretation it is going to be very difficult to come to any clear, objective conclusion. We simply do not know what the apostles would say if we were able to ask them what the proper answer is. We can find clues in Scripture that we can try to use to help us lean more one way or another, but we have to admit that the evidence is sparse enough that we would not think it terribly surprising or absurd if, were we able to ask, say, the Apostle Paul what the correct answer is, he gave an answer different from ours.
This is exacerbated by the fact that we can't even know if this method of trying to figure out the truth is the proper one until we first show that Sola Scriptura is the correct presupposition for interpreting Scripture. If Sola Scriptura is correct, then the proper way to figure out the answers to doctrinal disputes is to do one's best to interpret Scripture for oneself, making use of all the clues available, trying to infer the correct answer as best one can even in areas where Scripture is not plain or explicit. But if Catholicism should turn out to be true, this would be the wrong way to interpret Scripture. According to Catholicism, Scripture comes as part of a package deal which includes also an infallible Tradition and an infallible Church teaching authority (Magisterium). Scripture is meant to be interpreted within the context of the infallible Tradition of the Church and under the guidance of the Church's God-guided interpreters. The Magisterium of the Church constitutes a divinely-appointed human, visible Supreme Court to adjudicate doctrinal disputes. So if Catholicism is true, the Sola Scriptura method of interpreting Scripture is almost certainly going to lead to false conclusions, at least sometimes, because we will not be using the proper, God-ordained method for its interpretation.
So when we try to come to a conclusion about something like infant baptism on the basis of our own personal investigation into Scripture, trying to sort out the most likely answer based on whatever clues and hints we can find, without any reliance on an infallible Tradition or Magisterium, we are in deep waters, and the results of our investigation are going to be very subjective. If we know for a fact that Sola Scriptura is the right method for interpreting Scripture, then we can trust that God will overrule the obvious tendency towards subjectivity here and ensure that, if we do our best, we will end up with the right answer. And, when we find ourselves in dispute with lots of other readers of Scripture who come to different conclusions, we will assume that they are objectively wrong, even though it is hard to prove on a human level that one's own conclusion was arrived at in a clearly, objectively-better way than the alternative conclusions. (After all, in disputes over the meaning of complex and subtle literary documents, it is notoriously difficult to separate objectively-better interpretations from differences rooted in personality, background, bias, etc., and the Bible is certainly an extremely complex literary document, written in ancient times in ancient languages by many different people in ancient cultures, very alien from our own in many ways, over thousands of years, containing a variety of literary forms, etc.) But when we throw in the fact that we first have to prove that Sola Scriptura is even the proper way of proceeding to begin with, I think it must be concluded that there is simply insufficient data in Scripture available to do what Protestants try to do with it. To a large extent, Protestants are trying to squeeze the milk of a complete and detailed doctrinal system out of the stone of a Scripture that simply cannot yield what they want from it.
Conclusion
I think that Catholics should be more careful in their criticism of Sola Scriptura not to caricature the viewpoint. To conflate the idea of Scripture as the supreme doctrinal standard with the idea that people have a right to interpret Scripture in their own way is inaccurate and misrepresents what Protestants believe. However, I think that this caricature is based on some true observations and legitimate criticisms that, if stated more carefully and clearly, can constitute some significant and legitimate concerns and objections regarding Sola Scriptura without mischaracterizing the position. While Sola Scriptura does not imply that individuals have an intrinsic right to interpret Scripture contrary to the teachings of the leaders of their particular church, and so church discipline is not, per se, contrary to Sola Scriptura, yet, in practice, the lack of a supreme human doctrinal court combined with Scripture's lack of explicitness and clarity on many important doctrinal subjects does indeed lead to the conclusion that there is a degree of inconsistency between the practice of Sola Scriptura and the practice of church discipline. For a church to be able reasonably to discipline one of its members for rejecting or opposing the doctrinal positions of the church and its leaders, the church has to be able to show with objective conclusiveness that its own doctrinal positions are indeed the positions of Scripture. Since the Sola Scriptura method of interpreting Scripture cannot supply that kind of objective conclusiveness, there is often an unreasonable inequality involved when the church regards its own interpretations of Scripture as objectively superior to the interpretations of its allegedly erring members.
For more, see here, here, and here.
Published on the feast of St. Maximilian Kolbe.