There's a part of the story where demons are negotiating peace between a town and attacking demon forces. As soon as Frieren hears of this, she says the town is doomed.
Moral of the story is if your problems are caused by a group, don't expect a member of that same group to help you solve that problem.
The fact that the fictional characters are monsters doesn't mean they can't have been inspired by real life groups of humans who prey on human kindness. Europe is currently being flooded by such.