So from what I understand. Demons don't feel certain emotion this make some of their action which may seem barbaric, cruel to us human but does not cause any issue with the Demons themself. So that make a question, does that mean that they act upon instinct (kill thing that may oppose a threat to them ), search for food (since some chapter before, demons do consider human as food, like how we see killing cows, chickens for food) or simply they just do it for the thrill/fun (since they can still (maybe) have critical thinking skills as well as understanding of fun so by killing us for sport they can feel the sense of dominance)