@Samadhi_Overdrive
@Kireato
You also cry about physical pain, not just because you are sad or repentant (or resentful), but out of pure and simple physical reflex.
And although thank goodness i have never had the experience, I can say without fear of denial that cutting your own neck very slowly is very, very, VERY painful. Enough to make even a demon cry.
@VillagerC
Why can't demons live peacefully with humans? For the same reason if you put a fox in a henhouse the next day you'll find all the dead chickens and a fox with a full belly, not foxes and chickens playing happily and cheerfully with each other.
The demons in this universe are humanoid monsters that eat humans. Hard to make a deal when you're on the wrong side of the dining room table.