I do think certain games like Manhunt are kind of irresponsible, both to the people who play them and the industry as a whole. Obviously the vast majority of us can play these games and remain stable, but they do make a wonderful scapegoat.
GTA however, its part of the storyline, and any violence seems quite acceptable to me, after all, killing sprees, or even just resisting arrest usually ends up with riddled with bullets by the police, so its teaching anyone who'd played it that there would be harsh consequences for unlawful actions.
I'm with Rockstar games on good ol' Jack T tho, they were quoted as saying something along the lines of 'We thank our lucky stars for Jack Thompson, we might be concerned if we had someone sane and competent campaigning against us.'
Really tho, I'd consider the opinion of someone who was against violent video games, but anyone saying "reckless worldwide distribution of its murder simulation training products. This is just the latest killing incident prompted by your murder simulators. I aim to make it the last." Murder simulation training products? You could almost vaguely in some way pin that on Wii Manhunt 2, with it making you make stabbing motions to kill, etc, but GTA, ridiculous.
Also, Did Jack Thompson not, like everyone other 4 year old boy, chase his friends around the park making gun shapes with his hands and shouting BANG? I'm assuming he had to train to be the monumental tool that he is now.