Say you poll a bunch of Catholics about marriage and sex and find that the vast majority of them don’t believe what the Church says about it. Is this a failure of catechesis? Is it even a widespread rejection of the teaching on chastity? Sed contra: if you polled the same Catholics about the evils of racial prejudice or drunk driving, you’d probably see the same vast majorities supporting what the Church teaches (cf. ccc 1934 or 2290) but no one would take this as proving the success of catechesis or a widespread acceptance of Catholic teaching. It’s a coincidence. Church teaching on prejudice and drunkenness just happens to coincide with the beliefs of the world in the same way that it just happens to differ from them in other areas, and the success or failure of catechesis has nothing to do with it.
The supposed rejection of sexual beliefs is really just a point of difference that the Church has with a vaster unified moral system that is not named. We miss something when we blame the Church for lack of catechesis: the people she is talking at are following a different voice, regardless of whether it agrees or disagrees with what she is saying. Their attendance at Church – and even their acceptance of catechesis – is itself just as much a command from this other voice as the one that makes them reject chastity or accept the evils of drunk driving. In fact, their acceptance of various Church teachings might well be more offensive to God than their rejection of others, for the same reason that loving a woman for an ulterior motive is more offensive to her than simply not caring for her at all.
One insight that is never mined in the modern metaphor of the “cafeteria Catholic” is that one can only pick and choose in light of some standard, and this standard is the true morality one is following. Like all moralities, it is rigid an uncompromising on fundamental tenets, and it demands not only orthopraxis but right belief, though it hides this rigidity behind the mask of being reasonable or even “just the way things are”.