Speaking from personal experience, as a child I never felt the urge to cause violence from playing games rated T or higher. If you are me however, I know what is real and what isn't. I guess it all really matters on the personality of said child that you are associated with.
Yes, I do believe children should be allowed to play violent games, provided that they are mature enough to understand that what they are playing is not real. It is the parents' responsibility to make sure their child can handle the sometimes graphic material. Preventing children, especially older ones, from playing violent games encourages them to seek out the games at their friends houses or elsewhere where the environment may not be as controlled. In the proper context, violent video games are no different than angry music or violent TV shows or movies. They're just mindless entertainment.
I think kids should be allowed to play violent games. It is fine as long as they know that the games that they are playing are not reality and that they should not try to mimic the actions that they see n the game. As long as that is established, then everything is okay.
What are you teaching your kids if you allow them to play violent video games? That killing is okay. Do you not think that those images on the screen will be permanently seared into a child's mind? What will stop them from wanting to experiment with killing or abuse in real life. Is it acceptable until a human is hurt? It teaches kids that violence is a solution. Isn't that the last thing America needs right now is violence as a solution. NO!
There is a restriction on violent games, so in order for a child to play them, it has to be bought by a parent of older friend. There are too many children bringing guns to school, bullying, or being bullied and fighting. While I don't believe games are the cause, they certainly do not help and they should not be allowed in a child's toy box.
I agree with age ratings on video games. In general, while violent video games have no impact on violent societal actions (no viable correlation made to date, at any rate), kids are only ready for so much. Parents have to know their kids, and allow them to have access to things they are ready for, and mature enough to work with. Same goes for sexual content. There are simply things that kids are not ready to struggle with. Violent scenarios when kids are too young can cause nightmares, it can spur conversations that the kids aren't ready for. A lot of things.