Just using a rough arsed guess, I'd reckon that most of the psychological distress that can come from sex is the link to the ingrained sense of what religious organisations feel it is all about. As we are talking Catholicism, the sense of mea culpa that goes beyond people who believe in such things and into mainstream society.

Hence my comment above that if adultery wasn't frowned upon by those we are taught to put on a pedestal, it wouldn't be as much fun for those who indulge....

Assault is assault is assault, but consensual sex, if it leaves a scar, there has to be a proportion of blame attached to those who try to write rules on who with and when....