I know this conversation is a bit past its shelf life, but I felt the need to share a bit more about my opinion. The main reason I think your child should not play GTA is because of the moral corruption, not the violence.
This is where the conversation becomes deeper and more psychological. What is the line between moral corruption and violence? And, furthermore, is a child capable enough of understanding that not all violence is immoral?
For instance, were allied soldiers behaving immorally when they shot German soldiers? Meaning, if my son plays any number of WWII shooters, then is the violence "acceptable" because it involves winning by means of being an Allied soldier killing Germans? Or will that kind of play end up having a corrupting effect (aggression) anyway? I'm torn on this, but I lean toward "no violence".
(A more poignant example of moral violence that is beyond the scope of this discission is: Is a woman immoral for shooting a man trying to rape her?)
If there should be a warning on games, it should read, warning: children do not come with the knowledge of the moral implications of their actions. That being said, it's damn near impossible to keep such media from reaching your child (as the porn DVD has shown you). If you do have some time to spare, you should do some research on video games with reasonable violence that rewards "good" actions such as diplomacy, and downplays violence to be only a last resort for defending, since it could loose you potential allies. I would highly recommend that you purchase "Black and White 2", and sit down with him and make sure that he attempts to become a benevolent (as opposed to malevolent) deity. It's similar to how my dad got me a playboy magazine when I was younger. I know it sounds controversial, but my dad explicitly chose a magazine that simply had beautiful topless women in dignified poses with no text on sex. I honestly think there's no harm in nudity, but there is in the strong sexual content that is scattered throughout the web, and that magazine kept me from looking for it for a long time (believe me he WILL stumble upon it). I know you'll most likely want to continue debating (and probably chew me out for telling you how to raise your kid), so just add me to your friends list on slashdot and we can continue via email.
I won't chew you out because what you're suggesting is kind and helpful instead of condemning and critical.
Since I am a gay adoptive parent, I don't have the luxury of being merely a good parent. I have to be better than all the straight parents. This is because whatever troubles my son has are going to be attributed to his not having a "normal" family by some people. I dislike having that kind of pressure, but I accept the consequences of my choices. I don't think my son is ready for such an open-ended game like Black and White 2 yet. I have actually considered letting him watch the movie "Grave of the Fireflies" recently to show him that war isn't like a video game. Anyway, sorry to get too personal, but it's only to show you that I put deep consideration into the type of media that my son is exposed to. Is it impossible to have complete control over what he sees? Of course not. But I just don't have the latitude to be blase about it because the stakes are so high. Thanks for listening, and I hope you understand why I take all of this so seriously.