Not a flippant comment...... I blame Hollywood. I honestly do. They glamorize and hero worship mega violent law breaking cops, while at the same time portraying criminals as super beings with government like resources, who always lose due to the violent law breaking cops. The people in the end believe this to be a vaguely true, even though in their lives they rarely see it, most cops are in fact fairly decent profess…
American culture as a whole places a ridiculous emphasis on empowerment through violence. It's everywhere; films, tv, books, music, punditry, news reporting, people's attitudes and idle conversation. A huge proportion of narratives resolve themselves through heroic violence. Often a heroic character will find inner strength through physical violence (and often inner strength means becoming murderously callous).
If you take a step back and look at it critically, it is rather absurd. In the real world true empowerment comes from intelligence and leadership skills. In the real world, having to kill lots of people would be very traumatic (at least for a well adjusted person).
I don't think it's as simple as violent movies causing violence. I think the real dangers come from the unspoken assumptions, the things that movies take for granted, which then become part of everyday thinking.