I disagree. Demons may or may not look human, but they are not human. They are alien to humanity - they have no conscience whatsoever, and they are sadists and liars at an inhuman level. If you ever met one, you will never forget it.
Quintessentially true.
I have a buddy who met Old Scratch twice. Told of how the first time it offered to buy his soul for rock and roll (really — though no sale) and the second time it made the room 20 degrees colder. Malevolence of this kind is beyond the imagination of humans. The evil of humans is never this purely evil.