Religion

is the requirement that priests be celibate.

It's an impossible requirement, since, as you say, priests are human.

And because priests are human many of them (perhaps as many as half) enter into sexual relationships at some point during their service. Most often these are with consenting adults, but even these need to be concealed from the hierarchy, which itself is practiced in looking the other way. This all fosters a culture of denial, of secrecy, of "I won't squeal about you if you don't squeal about me" or "people in glass houses..."

This aspect of the issue was brought up in the film "Spotlight."

Just to be clear, I'm NOT saying that celibacy causes child abuse or in any way justifies it. But what the celibacy requirement does is make many priests into liars and frauds. Much as prohibition led to political corruption, the celibacy requirement leads to ethical corruption.

And having an all-male hierarchy makes it all exponentially worse.