It may not be the main reason (which is believe is the tetraethyl lead mentioned in other posts), the effect videogames has had on violence is not trivial. Probably not for "outlet for rage" reasons, but simply because they are a powerful draw on someone's time. Spending time playing video games is less time left for loitering and petty crime.

I submit as "evidence" a bit of anecdata I like to call the "doom curve":

http://blogs-images.forbes.com/erikkain/files/2012/12/videog...