He wasn’t dressed like the villain, the villain doesn’t wear a bullet proof vest or riot helmet. There were ZERO spree killers inspired by Natural Born Killer. Juggaloos are nuts, much as I hate ICP you can’t really pick your audience. The Dendermonde attacker did not dress up as the Joker, just had died hair and some make up.
So far all of your “incidents” of life imitating art didn’t happen. Meanwhile out here in reality there are nutty people and there’s no torture porn in the Dark Knight.
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.