Good point JollyRoger.
Imagine if I decide to create a group of Talebans yelling stuff at people about religion and stuff you know. No matter I RP it "for fun" it might still be offensive to some, cos the memories of certain real tragedies are not far from us. Same fo Nazis. Europeans still feel sensitive about these topics, more than in other countries.
In a community based game you have to choose wisely what to do and what not, for your own enjoyment and the other's.
Even RPed racism might end up having a bad effect on someone. If you really want to do it aim at sci-fi races and species, like mutants or aliens.