If a game has a protagonist who performs reprehensible actions then the player will likely not be able to identify with the character and would then not find the game enjoyable. Each person has their own limits to consider. A game that is poorly written will probably not get played even if the subject matter is controversal. The "Grand Theft Auto" games did well because they were well written and fun to play, (or so I've heard) not just because they were controversal. Games where the goal is to rape people or kill inocents are best avoided in my opinion, likewise I would find playing a racist to be objectionable. If such content as murder, rape, and racism are present in a game then they should not be glamorized and probably shouldn't be made light of either (Though making fun of such things has been done before in shows like South Park)