Guns are certainly the problem, but not all of the problem. This, I think, is the key insight in David Shields' "Columbine Virginia Tech Fort Hood Tucson Aurora Newtown—An Etiology," a collection of quotes and comments recently posted on the Rumpus. Here is the nut:

The number of guns in circulation is certainly an element in the modern gun culture, but the cultural ethic that sanctions private violence is the critical element. Switzerland and Israel, where army reservists maintain their own weapons, have comparable levels of distribution. Yet those weapons are rarely used for private revenge or crime. Nor can we put all the blame for gun violence on the excesses of the contemporary media. European and Japanese audiences consume violent American films as avidly as we do, and their own studios produce highly successful ultraviolent movies without comparable national homicide rates.
There is something profoundly American about mass murder, something in the structure of its culture that this kind of violence answers or expresses. If we do not address this deep structural flaw, then gun control will only provide a superficial solution.