If they're going to go the "Demons are actually kinda-sorta-okay-ish" route, there's also an anime meme of "miasma", that while demons COULD be reasonable, friendly, peaceful, whatever, their very existence is toxic to humans and human-friendly nature. Just breathing, as a demon in the human lands, will poison crops, give bunny rabbits cancer, and encourage the spread of the plague.

It allows for "noble demon" archetypes and friendly demons, while still maintaining a solid "us or them, literal existential threat" element to the demonic hordes, and a solid reason to not want them moving in next door.