Thanos was a great villain by this standard. He had lived through the suffering and collapse of his homeworld due to overpopulation, so his motivations actually made sense.

Meh, there are plenty of people in the real world who just want power and money for themselves, who will shit on anybody and anything to get it and teach others to hate on people for just being different in order to gain power. I don't think it's at all implausible that absurdly nasty and selfish people exist.

That can be tricky, though. Done well and you get a villain like Gul Dukat. Done slightly less well, such as with Killmonger and the villains from both Incredibles movies, and you have to make them at least resort to "for the evulz" methods to prevent the audience from sympathizing with them, and even then you may be left with a broken Aesop at the end.