Part of this in my experience comes down to something we tend to talk about a LOT, but put into practice much less frequently: separating IC and OOC. If your character is a huge racist jerkass, people just sort of -assume- you are too. It gets more muddied the less extreme the example of 'particular deviance/weirdness' is.
Look, we tend to talk a big game about keeping IC and OOC in their own corners, but as a hobby we -suck- at this. Maybe not all of us, but I think I can safely say that there's a nice bell curve between 'what separation?' and 'picture perfect model of person keeping things distinct'.
Until we're willing to roll with the idea that horrible characters who do terrible things are not by default played by awful people, I think this is a losing battle. We're too quick to take offense to... just about everything, and we as a hobby have way too long a memory for these things. I think this is unfortunate, but I think that it's the nature of the beast.
My two cents.