I posted a response similar to this on DailyTech and I'll make the remarks here as well I guess. First off, I don't agree with Thompson. To me, these people have issues to start with and all they need is a catalyst. Sure, a video game... or a movie... or seeing something horrific (i.e. real life... we can't outlaw that, can we?) could just make these already messed up individuals worse. But when it comes down to it, the problem was with the person and unless you plan to keep the mentally unstable in a bubble for the rest of their life, you're going to see these events.
So now, the main problem that ol' Jackie Boy is having is that he's not presenting everything logically. He's throwing the proverbial spaghetti at the proverbial wall and hoping that it'll stick and will be enough to cause people to notice. Unfortunately, for some people, the spaghetti is enough to jump on the ol' bandwagon and raise arms (heh) against violence in media.
What Thompson needs to do is to show that by immersing yourself (i.e. a "hardcore gamer") in violence (note that although I used video games a couple words ago, this could be any high level of violence in an event), it causes long-lasting effects on how you think and, most importantly, respond to situations. Showing this could directly link even (heavy) High School Counter Strike playing to 4 years later in college. But if he can't, people right now have the idea that it's a direct effect... i.e. someone plays CS, snaps and decides to play count the head shots with real people.
The problem with everyone's argument against Thompson, is that they aren't proving him wrong. I mean, I could go and say, "I've been playing video games for years and I'm not shooting people." But are you admitting to being a mentally deranged person? Are you putting yourself on the same level as these killers? No, it's also unfortunate that Jack simply does not realize that his argument is too basic... he needs to start mentioning that these kids are messed up to begin with. You could then go on to mention how this age (especially with the high acceptance rate of the Internet within the past 8 years) has become a true media age as it's hard to "disconnect" yourself from the world... and violence either faux or real. Until he mentions these (fairly obvious) reasonings, he will be nothing but a jester, because he's too generic.