According to Police Commissioner Raymond Kelly, “James Holmes said he was the Joker, enemy of Batman.” But according to your theory, he would have been equally likely to have unloaded on the crowds attending Magic Mike or Moonrise Kingdom. Your problem is you’re tasking science with proving a 100% causal relationship between environment and behaviour, something which is impossible. If that’s your standard, you might as well open the floodgates for free enterprise to market all the drugs, porn and violent conditioning from infancy to adulthood. But we don’t do that. Why? Because where science is useless, a little God-given thing called common sense is supposed to operate.
Here’s some of the completely neutral but really entertaining scenes from the Dark Knight. Joker stuffs a bomb into a wounded bank employee’s mouth; A man’s face is filleted by a knife; another’s is burned half off; a man’s eye is slammed into a pencil; A bomb is crudely stitched inside another man’s stomach, which subsequently explodes; a trussed-up man is bound to a chair and set alight atop a pile of banknotes; a child is terrorized at gunpoint by a man with a melted face. I see no point in viewing torture porn. It’s neither uplifting, nor redeeming, nor entertaining, nor even interesting.
It’s not a theory it’s reality. Nutters pick random stuff to go off on all the time. One nutter tries to imitate the assassination that fails in Taxi Driver doesn’t mean it’s the movie’s fault, Hinckley is nuts. Last year in Tucson we had a whacky shooter people tried to blame on all kinds of stuff, mostly conservative media figures, kind of all fell apart when it was revealed the Loughner didn’t watch TV. Everybody wanted to blame Doom for Columbine, completely ignoring the fact that there’s no bombs in Doom and high school kids don’t really look much like the demons you kill in Doom.
Science has already proven why these people go off: because they’re insane. Psychotic people tend to be obsessive. Which means they tend to be super fans of something, but if that thing didn’t exist they’d be a super fan of something else, because obsessive people will always find something to obsess on.
Common sense says that hundreds of millions of people have watched these movies without killing anybody, so blaming the movie for the behavior of ONE person gets a little sketchy.
You don’t actually see most of those things happen, it’s mostly off camera and implied. It’s not torture porn, it’s dramatic tension. Bad guys need to be bad guys.