I Could be a Bad Catholic
Protestant Christians generally think our churches are human institutions. I like my little Episcopal church, but I don't think it's any more legitimate than the Catholic church down the road or the Bapist Church a few blocks over.
This is not the Catholic Church's self - understanding. It teaches that it and it alone is God's favored institution on Earth. It can authoritatively define doctrine, and it does so infallibly. I intermittently feel drawn towards Catholicism, but I can't assent to everything it teaches. Some of the RCC's teachings seem patantly false, others immoral, others apparently contradict previous teaching. And, being bound to believe so many dogmas would be psychologically difficult for me. If I discovered one of them was wrong, even in the smallest detail, then the church would not be infallible, and thus the whole religion would be false. It's the same way I feel about most articulations of Biblical inerrancy or infallibility.
But, most of the Catholics I meet do not feel this way about their church. They probably disagree with the church about half a dozen things, and this doesn't bother them. They happily have premarital sex and take contraceptives; they don't know or care who was anathematized by the Second Council of Nicaea. If I was raised Catholic, I could easily have this attitude: I could go to a Catholic Church but not be an Orthodox Catholic. But, for good or not, I can't convert with that attitude.