There have been a few books on the subject. Probably the most influential of which is Grand Theft Childhood: The Surprising Truth About Violent Video Games and What Parents Can Do.What science shows that?
And the prepper thing is odd....I'd think they'd stay home, not go out looking for trouble.
While most agree that playing violent video games cause a minor increase psychological and physiological aggression, there's no conclusive link between games and violent behavior (like school shootings) despite constant arguments to the contrary. Also, pretty much all of the studies that DO link the two are considered by the scientific community to be flawed mostly due to things like small sample sizes, use of outdated media, and poorly defined terms and statistics.
Basically, anti-gaming rhetoric is just as asinine as anti-gun rhetoric.
On the subject of preppers, they just seem paranoid and jumpy to me. Let's also not forget that they're eagerly awaiting a SHTF scenario so that they can show off their foresight and skills. Furthermore, and let's be honest here, despite all of the "sheepdog" rhetoric, a lot of these guys would be the marauder type. As such, I sometimes get the feeling that even in a small-scale WROL, like a natural disaster, one of them might shoot at me or someone else simply for entering their turf on the grounds of "self-defense".
Despite that, I'm really not concerned about them much at all. I'm simply more concerned about them than anyone else because I'm not really concerned with anyone else.
Perhaps I should have worded the original "the only people I have any real concerns about" meaning concerns (however small or unlikely that I may face them) that I feel are realistic in a given scenario and not just imagining the worst case scenario.