Central to Protestant self-understanding is the notion that Protestants are the "Bible people"; the ones who are Bible-centered (as well as "gospel-centered," of course) and who reject the "traditions of men" and arbitrary rulings of a powerful ruling class with a vested interest in the status quo. Many Protestants assume that they more or less have a monopoly on love and respect for the Bible.
Clearly, the abovementioned self-understanding is no longer held universally among those who call themselves Protestants. However, for Evangelicals (and particularly, for Calvinists), who regard themselves as the true inheritors of authentic Protestantism, this identity is as strong as it ever was. Ironically, it is this very identity that prevents Protestants from coming to a greater understanding of the Bible, as I shall discuss below.
It should be remembered that Protestantism was born, as it were, as a reaction to the Roman Catholic Church. Because of this, the early Reformers had to commit themselves to hermeneutical principles (presuppositions, for the presuppositionalists among you) that justified their reaction against Rome, whether or not these principles accorded with internal biblical testimony. The obvious first step was to deny the authority that Roman Catholicism attributed to sacred tradition. Not only did this provide some kind of a leg to stand upon, it also reinforced the perception that Protestants had a high view of the Scriptures because it was their ultimate source of authority. This presupposition also carries with it a presupposition of the sole sufficiency of Scripture.
The belief that one could deny the authority of sacred tradition and question the interpretation of the established church created further problems. On what basis could the Reformers legitimately do so? How did they know the interpretation of the Bible by the Catholic Church was wrong? The only viable solution to this dilemma is to assert that Scripture at these very critical points relating to salvation was self-evident. From here, we get the presupposition of the perspicuity of Scripture.
It is the presupposition of the perspicuity of Scripture, along with the identity of Protestants as the "Bible people" that has been so self-stultifying for Protestant understanding of the Bible. In short, if Scripture is clear (at least at important points) and you are part of the tribe of Bible people who are devoting to studying the Scriptures intensively, then it stands to reason that you believe your tribe understands the Bible correctly. The problem is, how do you explain the fact that other tribes disagree with your interpretation at different important points when you have affirmed the perspicuity of Scripture? If you're convinced that you've understood the Bible correctly, the only logical conclusion is to suggest that the other tribe is simply ignorant about Scripture. That is, if they had the devotion to Scripture that you did, and because Scripture is clear, they would come around to your understanding. No wonder that Calvinists like to perpetuate the myth that most Catholics are biblically illiterate.
Of course, there is the slightly disquietening thought that there are some who disagree with your understanding of the Bible that have studied the Scriptures diligently. One way around this is to simply claim that those people have simply been brainwashed by that Great Satan, the Roman Catholic Church and are parroting exactly what they hear from their evil overlord. The other way is to reaffirm that you are in fact part of the tribe of Bible people, that you cherish the Bible, that this person stands against you, and as such, they stand against the Bible. In short, if they were being honest with you and honest with themselves, they would quite humbly admit that you were right all along. Quite naturally it would be that way. After all, you belong to the tribe of Bible people ...