I'm hopping in here at the last page without reading the entire thread, so read the following with the grain of salt.
Of the younger generation (30 and under), which I am a part of, I find the single biggest contributing factor to genuine enthusiasm in firearms to be pop culture as a whole, but more specifically video games. I grew up playing Battlefield 1943, Bad Company 2, the Modern Warfare series, and the Black Ops series.
Some of these games emulate the strengths and weaknesses, sounds, manipulations, and modularity of different platforms quite well, and serves as a great introduction to firearms and translates that interest quite well into both the collector aspect as well as the shooting sports (2-gun, 3-gun, ipsc, etc.). It can't be understated how much video games has done to educate this younger generation on many of the nuances of firearms (the different actions including the differences between a standard self-loading semi-auto and a full auto, suppressors, mag capacity, caliber limitations, accessories, etc.), all of which results in a more educated generation even the ones that don't take an interest in the ownership or use of real firearms, which makes for a generation less indoctrinated by anti gun narratives.
I can tell you right now with 98% certainty I probably wouldn't be a Firearms Enthusiast at all if it weren't for the aforementioned video games.
I think drawing a direct link between video games and mass shooters is a big stretch at the bare minimum. If video games were the main contributing factor you would see these despicable acts being performed across most of the modern societies, not just the US.
I have far greater suspicions that the rise of these despicable acts in the US in particular have a lot to do with the over use/misuse of psychotropic drugs and the inaction to properly diagnose and treat mental illness.