Some games have no intentions other than violence and hate, however. GTA approaches an adult game in the same way as a five-year old who just watched pulp fiction. COD5 has an infamous mission in which you have to use a flamethrower, and the game punishes you for not doing so. No real reason for gameplay, they just like to force the player to burn people alive, and reward them for doing so. Games like garrys mod, portal and psychonauts are determined to make a good game, rather than pulling people in with violence and controversy. Even left 4 dead 2 went a bit far, and it's a worrying trend.
I question the games you cite, and the reasons you cite them with. First off, I don't think applying the word 'intention' to a game is a sound application. Does a game have an intention? What is that intention? I would say it's entertainment, but that's such shaky ground that it's far away from stable, usable, evidence.
Secondly, I'm not so sure what COD mission punishes you for not using a flamer (directly punishing), and I'm a bit confused as to why you didn't replace that with the far more infamous airport scene in MW2. Regardless, I think you're taking it out of context, where it seems much more vicious then it is. I believe you're referring to the mission in which you storm the beaches of Pelileu Island (however you spell it), in which you are advised, not forced nor punished for doing otherwise, to burn the Japanese out of cover. I've sniped people out of those trees, it's equally easy.
Thirdly, I see very little logical footing amidst a lava flow of opinion in this one. Simply put: Intentions can't be tacked on by a game, and if they were to be, it certainly wouldn't be by a single player. Side note: I'm sure that you're aware that Garrys mod can have far more cynical uses then many care to think of.
Finally, I hope I'm not the only one who believes this, but I think the L4D series does a nice job of carrying a running joke of the zombie apocalypse. I don't see it in any way as serious, rather I see it as making a joke of what would happen in a satirical zombie apocalypse, which itself is a form of satire.
Apologies to come off harsh on this one, but I think this is exactly what the study was meant to diffuse.
Side note, 900th post :O