It's interesting that we find links between environment, habits, and behavior in every other facet of life, but--somehow, repeated simulations of visceral violence (violent video games) are an exception.

This isn't a simple thing to measure. Players of violent video games have diverse environments, social supports, and other factors. These mitigate the effects of playing these kinds of games; in other words, while the games may encourage violent behavior, person A with a stable environment and strong social supports may not be effected in the same way (or enough to measure). Person B with a different environment and fewer supports may exhibit violent behavior. Some studies may claim to account for these, but that should be met with skepticism and rigorous discussion.