Our gun culture literally has a Wikipedia page, I'm pretty sure it's a thing. You also don't get to pick and choose only the "good" parts of it to include, it simply doesn't work like that. Your YouTube videos are stupidly anecdotal and I can find just as many of people being irresponsible with guns and having fun with them with the boys at the range (it's not only being stupid with them that's a problem, but treating them like some kind of bonding experience).
In any case, here are some actual academic papers that show through data that there is a clear and pervasive link.
Findings suggest most school shooters come from a social setting in which firearms are a crucial leisure activity and hold meanings of affection, friendship, and bonding.
https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0322195
I really want to stress the affection, friendship and bonding parts. Guns aren't a problem but once you start building your whole personality around it and feeding that kind of environment to your kids, it becomes problematic.
More permissive firearm laws and higher rates of gun ownership were associated with higher rates of both school shootings and active school shootings after controlling for critical covariates.