I thought hating on furries was a 4chan meme that became a tiktok meme.
But I've a few reasons why that meme may have gained traction. Firstly it's not a sexuality like homosexuality. It's more of a fetish, and people make fun of fetishes all the time - see feet, or, idk, midget. I'm sure some maintain its not sexual, but the community overwhelmingly is. Second, it has associations with beastiality. Now I'd assume the vast majority of furries don't harbour sexual attractions to real animals, but it's certainly on that side of the Venn diagram, which may cause some concern. Finally people involved generally seem to be social outcasts. You don't see many captain of the football team furries or cheerleader furries. If school kids are already picking on the weebs and the nerds, finding out some of them dress up like animals and hang out is fuel for the fire.
As for calls to killing furries, I'd wager the majority of that is just joining in on the meme. I'm sure furries would get bullied at school, but as for vehement violence I doubt it transcends the bullying that the D&D kids receive. Not that I condone any violence or bullying towards anyone, furries included. But if you were wondering why people dislike em, maybe this helps.