Most Catholics have heard the terminology, "Cafeteria Catholics," whereby they claim to be Catholics, but only accept things which are comfortable to them. Often with things like artificial birth control, abortion, etc. such Cafeteria Catholics pick and choose how far they want to accept the Church's teachings on these maters. Can these Cafeteria Catholics truly be considered Catholics at all? When someone decides for themselves that they will not follow a given teaching, have they not broken communion with the Catholic Faith?
Then we come to perhaps the ultimate Cafeteria Catholic... Martin Luther. At least Luther was honest about it though, he allowed himself to be split from the Catholic Church officially. But consider Luther... he "protested" against certain Catholic teachings, not the least of which was that over Indulgences. What if he had remained a faithful Catholic throughout all this? Once the Church tightened up the policy on Indulgences, Luther could have been viewed a hero by all Christians! Instead, he drew his line in the sand and separated himself from the Church... getting more and more vile and obstinate as the years went by. So, now the only ones who see him as heroic are those who followed him out of the Church. Since the Lord desires we be one, just as He and the Father are One - there was absolutely nothing heroic in separating the Church as he did. Luther essentially began the concept of "Cafeteria Christians," who pick and choose which doctrines they will follow. Others followed Luther - dissenting even further from the things which Luther dissented against - so much so that we end up with literally hundreds, if not thousands, of "denominations" which ALL have some level of dissent (or "protest") from the One, True Church from which they have all separated themselves from.