There is good and bad in everyone. That's why most christian religions assume that everyone will sin and will need forgiveness. That's also why some people feel a need to mock religion, other people, etc. People get a good feeling from making others suffer - from a good safe distance.
Sad but true.
I know I have this tendency, but back when I played DII I limited my PVP to trying to ambush PKs with overbuilt characters. Kind of a Dexter-ish thing to do. Didn't make it right, but I felt better about smacking the bullies around rather than others who were just trying to win PVM.