I don't have any real moral qualms about playing an extremely racist character in theory, but I do have a problem with it in practice, mostly out of deference to my fellow players. Interparty conflict is something we just generally avoid with my group, and I'd hate to unduly influence what characters people design simply because I insist on my own PC acting like a raging asshole.

My main group through the years tended to at least pay lip service to the idea of racism in Shadowrun, although like most things born out of human vileness and ignorance, it was played mostly for laughs. Racism is written explicitly into the system (or at least it was in earlier editions, I'm not a 4e expert) but tends to show up rarely in actual play-- you'd be hard pressed to find a sympathetic npc in a module who was racist.

But taking the fluff assumption that most people in the world are fairly racist against other metatypes, it was pretty common for us to play characters who reflected that. It was more Archie Bunker/Sanford and Son than Birth of a Nation.

AFAIK, there was only one explicit Humanis supporter who ever posted on Shadowland: Buzz, whom I believe first made an appearence in the Underworld sourcebook. I hope the developers revive that character; the fictional arguments that ensued were both interesting and humorous.

N/M, there were others; Hugh Mann, REAL Brother, maybe more.