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 demons weren’t even negotiating peace. They were trying to infiltrate
The anime Frieren has the advantage of being very recent and incredibly popular with normies, but this isn't the first time when anime tackled the subject when the outside forces tried to mingle with the local town. I think the anime Shiki actually had the new folks being friendly and peaceful with the local town.
But the humans thought they were, that's the important part.
They only learned to speak our language(s) in order to better trick us and kill us. They learned about our penchant for peacefulness and used that as a weapon too.
The demons cannot "coexist" with humans because they never wanted anything remotely like that. We are food and play-toys to them. It is only humans who want peace.
This is exactly the same for Islam: they're allowed, by Allah!, to lie to us heathen. Anything they say to advance the establishment of the global Caliphate is not a sin, it is a duty!
Not really. The impt part is op didn't mention that part in his opening text, which leaves all your context and the fact the demons were faking it out.
But yes, the demons in frieren can't be trusted. Can't wait till they animate the macht arc and leftists scream
I didn't mention the context because i thought i didn't have to explain this.