We can all agree she was an awful person in pretty much every way, but most of the other villains (some who were objectively worse than Umbridge, like Voldemort and Bellatrix) have solid fanbases. There must be a reason why Umbridge is hated a lot more than these conventionally more 'evil' villains. Why do you think she's so hated?

EDIT: Going from what people have said, it's interesting because Lucius is my favourite character, and he too seems to resemble the real life wealthy stock who are heavy lobbyists, influence government policy, but may well have far-right sympathies. But Lucius isn't nearly as hated as Umbridge (I know he's disliked overall, and I personally love to hate him, but he isn't hated with such passion). Maybe, from what you guys are saying, it's because we're less likely to encounter a Lucius (or any other HP villain) than an Umbridge?