Furries really aren't THAT bad, at least in the context of all the different paraphilias out there, there's certainly worse kinds of fetishes.
Furries are fascinated by anthropomorphism, the blend of human and furry animal features. They don't get off on beastiality or anything like that. They get off on erotic furry themed art (either involving original characters or licensed ones, with Sonic and Star Fox characters being the most common) and the more hardcore like to f*ck in fur animal suits.
But the worst thing about furries is how they absolutely
dominate deviantArt with their terrible artwork.
They also tend to be not very bright. Which I think combined with their alarming growth in population was a bigger reason people pick on them than the fetish itself, now it's just something to do because people on the internet are bandwagoning idiots.