Well said. It's not that they "hate" him, otherwise they'd drop the story. It's because Gwen exist. Gwen represents "freedom" for Nain and so, everything Amon is seems antithetical to what Gwen is. For that, they must "hate".
It also a trend to hate "the other guy". If you look through many BLS similar to this, you'll either see the same people or some words. Quite cumbersome...

I genuinely don't understand the amon hate in the comments. Idk how else the author is supposed to let y'all know he's NOT human and doesn't understand all the things humans need. like empathy and consent. like I understand, the sex scenes can be rough to read. I do feel uncomfortable as well but rather than hating amon for his actions I feel sad for both parties. personally I can tell how much amon adores na-in and it's painful to watch how he keeps hurting and stressing him out simply because he does not understand what he's doing wrong. and na-in, oh my poor boy idek what to say, I feel so much for him. I wish he could have it easier with amon but as I said, amon just doesn't understand as much as I'd love for him to, he's genuinely trying his best though. truly unfortunate.