Films and computer games are hardly bastions of "social conservatism". They do however depict the heroic, and on some base level that appeals to people (especially men). So it's good for business. Is this last redoubt of heroic values really the cause of the mass-murdering nerd? I'm skeptical. Suppose you removed this outlet for masculine fantasy (to be replaced with something that attempted to inculcate progressive values more systematically, I suppose); who's to say that school shootings would go down, and not up?
Impressively bleak view of manhood this: ; if men don't have their fantasy 'outlet' where they can channel their violent impulses, then they're more likely to go on shooting sprees. Imagine if that was a proven fact, what would this say about men's nature? I'm very critical of masculinity, but I'm a bit more optimistic than that about what would happen if we curbed some of this stuff (or at the least started questioning it more).
I mean in a way, I can see your line of thought (given that we're nowhere near to agreeing on what these values might be), but does that mean we shouldn't bother trying to replace them with more progressive values? To me it sounds a lot like that argument that if you took porn and prostitution away from men as an outlet, there'd be more rape, so we'd better not! Which sounds like a horrible excuse for defending something that men simply feel entitled to do and want to continue doing, a way of justifying harmful behaviour, abstaining from responsibility and dodging criticism.
Fantasy is never just fantasy, it always has real-world repercussions. Obviously its not as simple as 'heroic values in video games and films cause the mass murdering nerd', and I'm not campaigning to ban GOT or whatever, but like you say, its 'good business' so there's no brakes on any of this stuff and it has a massive psychological effect. Makes sense to look at the connections between it all at least.