There are fundamentalist psychopaths in every religion in the world. Every single one.

He's really sort of the devil. He's completely emotionally detached. He has no empathy. You find that in psychopaths. It's about power with Voldemort. It's an aphrodisiac for him. Power makes him feel alive.

Psychopaths know the technical difference between right and wrong - which is one of the reasons their insanity pleas in criminal cases so rarely succeed they just fail to act on that knowledge.