My argument supporting violent games (not neccesarily uber-gore, e.g. GoW times two. they need some type of storyline) is that you can either take out your frustrations on incorporeal ones and zeroes, or very corporeal, and very harmable people. There is an obvious, and distinct difference between a video game and real life. (Now, do bear in mind that I don't think that those under... 8-10 should be playing gears of war or Bad Company, but still. banning of a game in its entirety?)
1) in RL, there are no Covies (halo). you cannot kill evil aliens. you would not be able to survive a 20ft fall unharmed. you would not be able to run around with an MA5B, pouring ten pounds of lead into everything that gets unlucky enough to cross your path. in Halo, you can.
2) (Mercs 2) We are not at war with the Chinese in Venezuela. You cannot order in an Nuclear Bunker-Buster airstrike on the UP headquarters in the center of Maracaibo. You cannot fall from ten thousand feet and survive (ditch a heli up high). you cannot fall from four hundred feet and survive (that's about min height for terminal velocity - around there, anyway).
3) (CoD4) There is no way in hell a sniper will shoot the prop turbine on an in-flight helicopter, and take it down. it's too small, moving too fast, and there is a much larger, much steadier, much more effective target a foot and a half below it. the engine (which snipers can do). [I don't play this game enough to know any more aguments about it, really. just wanted to touch on a ps2/3 game, instead of all 360 games]
4) there is a higher rating than M, at least in the US. it's Ao. now, judging by the comments earlier, Australia doesn't use this. but it is also a death sentence for a game.
5) in a game, you can hit the power/reset button, and evey single thing is unharmed. there is no grieving mother. there is no crying little sister. there is no father who tries to be strong for his family, but really is just as sad as the rest. no next of kin need notifying. no ambulance need be called. no medical bills need paying. no medevac is called. no fire is hitting the UH-60 trying to save a guy with a bullet in his gut. there is no reprecussions from it. that is why people act like they do in those games. they know they can't do it in real life. that's why they do it in the game. it releases frustration, clears the mind, and let's a person relax when they've had a hectic, harrassment-filled day.