While I don't think violent video games are the driving factor behind gun violence, I think they have to be part of the conversation. Young people nowadays spend unhealthy amounts of time playing these types of games (i.e. CoD, MWx, etc.). To the point of having addictions, in some cases, and at surprisingly young ages. Some people live more in their augmented reality than their real lives, and I don't think that has a positive influence on their decision making process. Case and point, if video games have no effect on you psychologically, why does the military employ the use of Xbox controllers to operate their drones? "Hey soldier. Just drop those bombs on that target over there. Think of it like you're playing Modern Warfare!"
Then Hollywood steps in and portrays gun violence and killing as cool and hip. Yes, some people do take movies and television a bit more seriously than they should. They create unrealistic gun fighting scenes and getting shot never seems that bad. People dream of emulating that movie bad ass, taking Hollywood special effects and turning it into reality. How many accidents are caused by people trying to perform something they saw on tv?
Just because you are a logical human being who is fully capable of separating fact from fiction doesn't mean there aren't idiots who exist in this world who take television and movies a bit too seriously. When their entire everyday realities are being replaced by augmented realities, someone is bound to get them mixed up. Factor in some sort of mental or psychological disorder, sub-par parenting who use television and video games as a way to babysit their kids and possibly a trigger point, such as a divorce or lack of fatherly role model and you have a recipe for anything to happen. Top it off with possible anti depressants and/or anti psychosis medication and you have trouble waiting to happen. Give that individual access to firearms, next thing you know you have a Connecticut tragedy on your hands.