Some certainly are.
Probably not as many as you think, though.
There is also a pretty big continuum between the Archie Bunker types of the world... well-meaning but nonetheless offensive and hurtful out of their own ignorance and stupidity... and John C. Calhoun, ones with deep ideological commitments to hatred and discrimination.
Ones they are quite open about.
But that kind of nuance is not what online politics is for.
Online politics is for feeling angry. Because feeling angry is fun.
Nothing gets the blood pumping for a violent, chaotic species like ours by evolution like a good political flame war. Our lives have become so predictable, safe, and anodyne otherwise that we have to invent things to get angry about to feed our caveman brains.
A thousand kudos for a John C. Calhoun reference