My point is, if you are going to kill somebody because they are pure evil, then their being a human or a demon is irrelevant. If they are human and they are pure evil, they shouldn't be treated differently than demons who are pure evil.
I'm all for shooting them, btw. It's just the inherent hypocrisy of sparing human-shaped monsters while casually slaughtering the monstrous-looking ones that bothers me.