when we all, should, know that it’s horribly wrong and awful. [sic, the word "should" shouldn't be between commas]

This assumes two things:

1. Some kind of universal, inherent and self evident morality; None of these things are true, as evidence by the fact most people do believe murder is wrong, yet there are wars, events entirely dedicated to murdering people. People do need to be told something wrong is wrong in order to know so. Maybe some of these people were never exposed to the moral consensus or, worse yet, were victims themselves and as a result developed a distorted sense of morality;
2. Not necessarily all, but some of these divergents are actually mentally ill - their "inclination" isn't a choice any more than being schizofrenic or homosexual† would be. That isn't a defense to their actions, but a recognition that without social backing and help, they could probably never overcome their nature.

† This is not an implication that homosexuality is in any way, or should in any way, be classified as a mental illness. It's an example of a primary individual characteristic not derived from choice.