Is it more terrifying to think that evil comes only from humans?

While we’re on the subject of the Devil, I thought I’d ask this question. When something or someone really evil comes about, people often blame the Devil. The Devil worked through Hitler or bin Laden or those child molestors or those murderers. Only the Devil could do such evil. No human could do that; it had to be of supernatural influence.

But is it more frightening to think that this evil comes from nothing more than humans alone? I can see why Lord of the Flies was so controversial. It showed that all humans have the potential to become savage monsters.

It seems to me that the Devil is a personification of the evil within humankind.