Choire Sicha asks how we decide violence is crazy:

[P]eople commit heinous, antisocial acts of violence all the time and we don't think they're crazy. And on the other side? Most of society's "crazy people" (which range from perhaps you and I to a number of less "functional" people) don't actually commit violence. But in our minds, thanks probably to the TV, people are most crazy when they are 1. weird and 2. mass murderers. But then you have to start asking hard questions, like: is bin Laden a murderous monster who knows what he's doing? Or is he "crazy"?