BTW, what would your family do if you were the victim under the same circumstances?
I wouldn't sue any stores or video game manufacturers. I'd ponder where we went wrong as parents, if there was anything more we could have done; I'd mourn what my son had done and what he had become; I'd grieve for the families of the victims; and I'd try, somehow, to carry on. But I certainly hope I wouldn't use it as an opportunity to extort a million dollars from Wal-Mart.
As far as telling reality from fantasy, every play "cops and robbers" as a kid with REAL people on the other end of that cap gun? If you were the robber, did you try ever try to "shoot" the "cop"?
The technology has changed, but the genre is the same. Personally, I'm not comfortable with playing GFA myself, for the same reasons I never played the bad guys in "Command and Conquer," because when playing an alternate-reality game I don't like to pretend to be someone I find morally reprehensible (and it's hard to succeed at GFA by being law-abiding...). I don't have a problem with other people doing so, I just personally find it unappealing.
Yes, I've read Dave? Grossman's book
On Killing or whatever the title was, and I see the point he is trying to make but I'm very skeptical that the effect is real. Even if it is, that doesn't make the game makers culpable, unless you want to apply the same standard to crime-glorifying novel writers, movie producers, and TV actors.
And on a personal note, playing Halo against my best friends has never even once tempted me to sneak up behind them and shoot/slash/melee them...has taught me a bit about situational awareness, though, and if Earth is ever invaded by short aliens with squeaky voices, I'll be ready...come to think of it, maybe Halo is good training for those "mutant zombie" SHTF situations...