Violent games/ music/movies seemingly turn out violent people. However they do so because we have abandoned the perspective of morality, right and wrong as a taught concept.
Multi-decade gamer here. Metal fan. A reader of fantasy. And I never killed/maimed/tortured. Because I was taught the difference ann consequence of right and wrong.
It is all about perspective.
That said you will never convince me otherwise that overly violent games do not influence the weak minded or soulless.
My life sucks, badly. I’ve also made use of video games, movies, and books that incorporate violence. I haven’t killed anybody either.
As I said, it’s not a cause, but an indicator of the possibility that a person could head in that direction. I’m not aware of any of these nutjobs that didn’t give indicators of their prediliction for violence. Every one of them, over months or years, prepared themselves for what they did and let it be known, in some way, that they were the type to do this.