I mean, you're thinking of demons all wrong there. It's not about 'reasonable' or not, they don't think the same way we do. They're chaotic, they all have their own idea of what is 'right' or 'wrong'. And some of 'em do the wrong stuff on purpose because we're an entirely different species from them and they feel no emotional connection to us. It's like a kid stepping on snails to watch their shells pop.

For the bomb demon in particular, if you had a way to bring back his sister he might be less angry. But he just likes blowing shit up. You'd have to ask him after you bring back his sister.