Not knowing that you have a villain inside you, a hero, and a bystander is a lesson that everyone should learn.
What is the quote from Jingo, by Sir Terry Pratchett, to the effect of "when someone does something terrible, we want it to be one of Them, because if it isn't Them, then it is Us?"
“It was because he wanted there to be conspirators. It was much better to imagine men in some smoky room somewhere, made mad and cynical by privilege and power, plotting over the brandy. You had to cling to this sort of image, because if you didn’t then you might have to face the fact that bad things happened because ordinary people, the kind who brushed the dog and told their children bedtime stories, were capable of then going out and doing horrible things to other ordinary people. It was so much easier to blame it on Them. It was bleakly depressing to think that They were Us. If it was Them, then nothing was anyone’s fault. If it was Us, what did that make Me? After all, I’m one of Us. I must be. I’ve certainly never thought of myself as one of Them. No one ever thinks of themselves as one of Them. We’re always one of Us. It’s Them that do the bad things.”
Jingo. 1997. Pratchett, Terry. NY, London, and Ankh-Morpork: Harper-Collins. p. 205
"Evil is unspectacular and always human, And shares our bed and eats at our own table ....” ― W.H. Auden