I was just reading this new study that suggests behaving immorally in games might make you morally sensitive in real life.
It got me to thinkin' about how much I dislike acting immorally or violently in a game when I am presented with the option to either choose a "good" or "bad" path. In Fallout, I try to do the right thing by the inhabitants of the wasteland. In Mass Effect, I preferred the paragon approach, only going back through the titles to play the renegade options to see how the story or characters played out (punching that journalist in the face in ME2 made me feel like a right jerk.).
In games where I have to kill people in order to progress the story I don't feel anything because they are simply obstacles which must be overcome in order to progress. If I don't shoot the Russian bad guys, blow up the rival drug cartel's hideout, or take down the gangsters hot on my trial in the streets I die or can't complete the game.
I threw up a quick poll for fun.