What constitutes acceptance and adherence to the Catholic religion is actually very narrow — a very thin slice.
The Church cannot be deviated from in the slightest little bit either to the left or the right. Just as you can fall off either the starboard or the port side of a ship, so can you lose your faith in a variety of different ways. We all know the obvious widely accepted way of becoming a former Catholic — by refusing to live by the Church’s moral teachings or even denouncing them.
This is the way the vast majority of people lose their faith these days. They fall off the port side, so to speak. They are obvious, plain to see, and seem to be everywhere. And that is the danger — since this is the most usual route people lose their faith, many Catholics believe this is the only way you can lose contact with the Church. But you can lose contact by swinging too far to the other side. There are various people who are baptized Catholics who think they can say the Church is wrong about Vatican II, for example, that the Council promoted heresies and still consider themselves Catholic.