Back to the real issue here. Several countries around the world (Canada, Europe, some parts of Asia) have the almost, if not the same relaxed laws for guns (My friends brother owns enough guns to arm a smaller village, e.g. he has a several couples of assault-rifles, AK-47, M-16 etc..). Although the number of people compared to the amount of guns are lower in the rest of the world than in the US, but not by as much margin that would justify the huge amount of killings.
The only thing that i can come up with is that is a social issue, atleast to a certain degree. And no, it's not godless liberals, gays or gangsta rap, since the rest of the world is exposed to the very same.