Ok, I have much input for this topic. First off, I personally feel that violent video games relaxes me. But so does any sort of activity that causes a release of endorphins or adrenalin, playing those games, as well as some racing games that I like, have that effect.
Now, since I work someplace that sells mature games, often times to very idiotic parents. I must say that the ratings are not the problem. And passwords won't do anything, because the kids will simply learn what they are. Not to mention that most current gen consoles have parental controls that allow blocking of any ratings.
Ok now as for the parents, I think that they need to actually be willing to spend time looking into the games their kids want to play. A while ago I sold an xbox 360 and Gears of War 2 to some parents for their young child... not even 12 if I remember correctly. He also likes to play HALO 3 regualarly. They hadn't even known Gears was a M game, or what halo was like. But they still got it, even after noticing the violence and gore tag on the rating.
ESRB ratings are a suggestion. (I suggest you take a look at their site.) It is also voluntary, but most retailers refuse to carry any unrated games. And they even suggest that you find information on the game to make an informed decision.
I played many M and T games before I was at the suggested age limit. And yes, I do consider myself an aggressive person at times, but not do to games. I don't see much difference between violent games and playing with toy guns, GI Joe, or toy swords. People make their own choices. And pretty much all games do show a difference between right and wrong. Even though that is the parents job to teach and impress upon children the importance of those morals. Millions play the same games, only a few react violently and blame the games. Which seems more likely, there are a few screwed up individuals, or millions that are somehow screwed up and therefore wind up unaffected by a negative influence.