When it comes to a set of instructions, whether it be an employee handbook, assembly instructions for a piece of furniture, a law, or anything else that is intended to be followed, it is vital that it be communicated in a way that can be understood by the intended follower/s. If a thing cannot be understood by its intended audience, whoever wrote it is a failure.
Christianity, of course, has universal intent. While it is true that we are not all intended to become pastors, there is not one person on the earth who is not intended to receive salvation, adopt Christian morality, and have fellowship with both God and other believers. As such, it is vital that these aspects of the Christian faith be available to all people on the Earth.
And it is. Psalm 119 tells us that God's word gives understanding to the simple (v130), and that it is able to give us greater understanding than our enemies, our teachers, and the ancients (v97-100). God's word is intended for all, and thus can be understood by all.
"Not so", says the Catholic Church. Whereas the Holy Spirit is our teacher, at least according to 1 John 2:27, the Catholic Church actively discourages "private interpretation" of God's word. You have to submit to the Catholic Church's interpretation. Apparently, they do all the learning for you. Your job is to learn the stuff they tell you to learn, which more often than not is far more complicated than the Bible ever was.
But that's assuming you are a Catholic in the first place. As a Christian, who am not now, nor have I ever been a Catholic, I submit myself to the word of the Lord. I believe the scriptures are inspired by God, and that they are useful for doctrine, for reproof, for correction, and for instruction in righteousness. Furthermore, I believe that they are literally all that is needed for this. They make the man of God complete, and thoroughly equipped for every good work.
Catholics, of course, dispute this. There are a number of additions they have made over the past 1700 years, and they insist that their Church has the authority to do this. The problem? In order to intellectually assent to this authority (as opposed to accepting it just because I was raised Catholic, or because I am gullible enough to accept it just because they claim to have it), I must apparently learn Church history. Or rather, their revised version of it.
Now, every attempt to defend Catholicism from Church history falls flat on several levels. But let's ignore that for a moment. If Catholicism is intended for all human beings, as Christianity certainly is, why would there be such a wall raised around it to prevent people from joining? Why would God give the world a book that allegedly means the opposite of what a natural interpretation would have us believe it says, then set up a horrifically inept organisation to interpret it for us, but also make that organisation virtually impossible for the layman to understand, to the point where one must actually do absurd amounts of research just to confirm its authenticity?
The answer is obvious: He didn't. The Catholic Church is a fake. The Bible says exactly what it says. If the Catholic Church really was the one true Church, they wouldn't need a million convoluted excuses for why the Bible should never be privately interpreted, like every other pseudo-Christian cult on earth (e.g. The Watchtower organisation). They would just be able to hand you a Bible and support their views from it. Kind of like "Protestants" do. We can prove our views from the Bible because we get our views from the Bible. Catholics must avoid, discredit and even bash the Bible because they are in direct conflict with it.