So instead of some wonky thought experiment, one researcher decided to measure involuntary muscle responses, galvanic skin reactions, the whole range of physical indicators of emotions. He found something interesting: gamers are distressed when they shoot an enemy in-game. (Instead, the gamers reacted positively to... getting killed (in-game, of course). The reasons why that is so are explained in the article, but that is not what I want to focus on.)
Apparently, shooting an enemy in a FPS game does not provide the player with pleasure. It probably triggers some deep-seated ethical responses to violence. It would be interesting to see whether the response increases as games become more and more realistic -- that would mean that gamers are getting more moral teaching from modern, realistic shooters than from, say, Space Invaders!
I propose we make violent games as realistic as we possibly can, to educate everyone on the awful nature of violence!