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.

Games and players
A game is only a means to an end decided by its players.
Yes, there are truly reprehensible RPGs - like RaHoWa and FATAL. I could add Dragonraid to that list too, but you might disagree with me. But what is reprehensible?
In games I have run, I have tried to steer clear of things that affect my players personally. Being a long-time CoC Keeper and dabbler in games like Kult, it is sometimes difficult to come up with something that gives the players the same sense of unease as their characters should be feeling. It is far too easy to resort to events that have badly affected the players in real-life, but I feel that is far too close to emotional abuse/rape for comfort. Even so, you can sometimes step over the line by accident.
An example: I was running "Love's Lost Children" from "The Stars are Right" for CoC. The scenario involves torture, child pornography and sexual abuse by NPCs who are worshippers of Ygolonac. We had all played to gether for many years, and I thought the group could handle the scenario - all being over 21 and consenting adults. Unfortunately, one of my players (unbeknownst to me) had suffered from abuse as a child, and the scenario affected her very badly. It was a very embarrasing situation for all concerned.
However, in other games, I have seen players commit what would otherwise be regarded as flagrant crimes and nobody has batted an eyelid.
An example: In a D&D game, we were confronted with a creature that was being held as the main attraction in a gladiatorial circus. It was capable of killing armoured paladins with single blows and seemed to enjoy the killing. Most of the party were in favour of rescuing this creature, and in doing so assaulted NPCs, broke contracts and stole property. The dispute in the party about doing this almost split the group.
So, to answer your question: I think there are no reprehensible RPGs, merely reprehensible behavoiur in RPGs. You can roleplay a tea-party using FATAL. You can roleplay the Incident of the May Babies in Pendragon. Reprehensible behaviour depends on the gaming group.
Personally, I draw the line at rape (non-consensual sex of any kind), graphic descriptions of torture and insulting another player's beliefs in real life - not because these affect me, but because of their effect on the people around me. So, the ultimate reprehensible behaviour for me is not to consider the sensibilities of your players.