Well, we have elements of ideology, self perception, and purpose for nano-machines, multiple instances of zombies, magic, ogres, samurai clan warfare... All in all, a diverse group that tolerates many different ideals.
So the question is, what is unacceptable in role play? Obviously, limits are set by the individual, but what seem to be safe guidelines?
The only truly reprehensible RPGS I've noticed are ones that blatantly flaunt racism or misogyny (Racial Holy War, and FATAL respectively).
Vampire, though it deals with internal beasts and drinking blood makes it quite clear that although vampires have guided human history for centuries, the holocaust during WWII is all our fault. On the other hand, D&D seems to condone genocide against orks, goblins, kobolds and the like.