So did Catholic priests, and that didn't stop them from diddling kids nor the Church from helping cover it up.

I do not understand what you do not understand. People are capable of lying, to others and themselves. As of yet, there is no external influence with a proven mechanism of action that can fully prevent that.

If you need a book to tell you this is wrong, that may be part of the problem.

The same book has written instructions telling her she can't be a priest (Paul says this multiple times.) I'm not defending that, but if she can rationalize one instruction away, surely she can any other.

>I truly don't understand.

Moral licensing, the idea that if you perceive yourself to be morally superior in one situation you will naturally make immoral choices further down the line.

https://en.wikipedia.org/wiki/Self-licensing