Violent video games, Violent movies, access to firearms... all of these things get the blame. Whether any of them are worthy of the blame remains to be seen, McVey had none of those things and killed more people than Lanza. I would say that the Gun Free zones can soak up some of the blame too. Plenty to go around.
"I would rather be exposed to the inconveniences attending too much liberty than to those attending too small a degree of it." Thomas Jefferson