Because they've got nothing to believe in. They don't care about manners or any kind of church. It's not philosophy. It's not fancy. Because of their despair, the wrong thing is sometimes dire.
Estranged husbands ignore restraining orders and kill the women they supposedly love most.
And these are very obviously mysteries. Pick up the morning paper and try to figure out why a farmer would kill his entire family and then burn himself alive in his house. I hope there's no simple answer to these mysteries. I want to believe people aren't that easy to understand, that even we who believe ourselves sensible often don't know why we do some very important things. I want to find out why things happen, but I don't believe psychology has all the answers.