One canard I'm fed up of hearing from Catholics is that "Protestants" believe everyone should not only be able to study Scripture for themselves, but actually come to their own, personal interpretation. Recently, my Catholic friend even compared the Bible to the law. You obviously can't come to your own interpretation of the law, the law is the law. Break it, get prosecuted. Otherwise, we'd just live in an anarchistic society.
The problem with this argument is that I fully agree. You can't just come up with your own interpretation of the law. You can, however, interpret the law. How? Well, because it's written down. A good law can be understood by all who are intended to obey it, whereas you cannot obey a law you cannot interpret. Therefore if you want to know if what you're about to do is legal, you can in fact interpret the law yourself.
At this point, the Catholic might ask "then why do we need lawyers?" To this, I ask how does one choose the best lawyer? A good lawyer knows the law better than the average citizen not because the law is unintelligible to the average citizen, but because the average citizen does not study the law. If we spent as much time studying the law as we spent on our own professions, we could all be as knowledgeable on the law as a competent lawyer.
The Scriptures, much like the law, are quite sufficient to present God's message to us. This does not mean that we are sufficient to receive that message. There are many reasons a man might be unable to interpret the Bible, but the flaw is on the human end, not the Scriptural end. But the Bible is so perspicuous, it even tells us those who meditate on it will have more understanding than their enemies, elders, and teachers (Psalm 119:97-100), even if they are "simple" (Psalm 119:130). Perhaps this is why God commanded the Israelites to teach it to their children (Deuteronomy 4:9-10; 11:18-19).
The idea that we need an interpreter between us and the Bible comes from the sin of the would-be interpreters. This is true not only in the Catholic Church, but in other religions Catholics would agree are heretical. The Mormon Church believes they have sole right to interpret Scripture for us. The Watchtower Organisation likewise teaches that Scripture belongs to the Church as an organisation, not as individuals. The Catholic Church would agree that they are wrong. But the Catholic Church, by the same reckoning, is wrong to claim authority over the Scriptures.
When we read the Scriptures, we do find that the Catholic Church violates them on a regular basis. It is self evidently not a Catholic book, though they falsely claim to have produced it. Reading it for ourselves, we find no evidence of a papacy. Purgatory is absent. The Marian dogmas are nowhere to be seen. Even the real presence of Christ in the Eucharist is so easily disputable, it was disputed even within the Catholic Church right up until 1215 A.D., when the French monk, Paschasius Radbertus' doctrine of Transubstantiation officially became a Catholic dogma. Contrary to the Catholic Church's assertions, "Protestant" interpretations of scripture existed long before the Reformation, and for good reason: they're right.
Claiming historical advantage does not work, because aside from the fact the Catholic Church continuously evolves, "Protestants" have always existed throughout history. You can claim they were heretical if you insist, but they do exist. If you're a Catholic, it is your job to prove the superiority of your Church's interpretations over "Protestant" ones. To do this, use the same method as you would use on the law. That is, go to the words. God is a perfectly capable Author, and His authority exceeds that of any Church. Indeed, when Paul approached the Galatians, He told them that neither Apostle, nor Heavenly angel, had the right to change the Gospel, and that if anyone approached them with a different gospel, that messenger must be anathematised (Galatians 1:8).
My friends, the Catholic Church is that messenger. The Gospel the Galatians received is the same as that received by all the Churches in the first century: "For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: Not of works, lest any man should boast. For we are his workmanship, created in Christ Jesus unto good works, which God hath before ordained that we should walk in them."
Because God is a capable Author, the words in His book are quite sufficient for those who study it. Therefore, those who study it will come to similar conclusions to others. Differences in interpretations, when sincerely gleaned from scripture, will never be so major as the gulf between Catholic and "Protestant". The doctrines of Sola Scriptura and Perspicuity, far from promoting spiritual anarchy, promote a unity under God through His word. Thus, no one is saying everyone should come to their own interpretations, but that everyone has the ability to interpret it correctly. This is a vastly superior method of the Catholic Church, which puts "Sacred" tradition on the level with the word of God by word, but in practice, places tradition above the clear words of His Holy book.