TLDR: Frieren and Flamme's depiction of demons as pure 'evil' or like dangerous wild beasts with an appetite for humans doesn't paint the full picture, and various examples in the story demonstrate that demons are not straightforward antagonists as a lot of people like to praise the series for depicting. I've been having these thoughts for months now, regarding demons being irredeemably evil.. The way the series refers to and treats demons feels really messed up, considering they're seemingly intelligent and capable of communication. But the way Frieren says to treat them, and nobody really argues it, is "Ignore anything they say, they only ever speak lies, kill them immediately regardless of when or where".
Demons know that people can and will exterminate them because of their threat Demons know that people are very vengeful and will persecute them Demons know that people travel in groups and have quite strong warriors and mages So, if you put yourself in the place of a demon, what is the point of fighting with people at all?. Frieren 's demons are incapable of being sympathetic because of their lack of human emotion, and that makes them the perfect villains for the series. The overarching theme of Frieren is the importance of embracing emotions and bonds with others, with Frieren's character arc, specifically, being about her journey to be more in touch with the emotions of herself and others. As such, demons.