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.
In that Greek slavery was worse, yes. You'd much rather be a slave on a plantation than be one in the silver mines, being worked to death.