You can find videos of archers having fun at a range, why does that not cause school archings? You can find videos of drunk ass axe throwers having fun at axe throwing places, does axe culture inspire school axings? Fun doesn't cause crime, the crime is caused by deep socioeconomic issues that can't be solved by stopping fun. And fun != irresponsible without your painting it as "fun causes school shootings" especially when you differentiate it from stupidity yourself.

Your study doesn't actually account for the fact that most school shooters, being unable to legally purchase firearms, steal them from their parents, and therefore it's more likely by default that their parents are "gun culture" people by virtue of owning guns. That still doesn't mean their kids stealing their guns to commit murder is "gun culture." Causation != correlation and such.

Your second study basically says "the more guns around the higher likelihood someone can steal one." Sure, but places with more permissive alcohol laws also have more drunk drivers, should we ban alcohol?