I cant believe we are even having this conversation after the events of the last few days. People that intend to kill will do just that. Its fairly easy if one is determined even without guns. What about the madrid bombings? How about Norway where even the police arent armed – bomb plus guns.
About the culture thing. Natural human reaction to a grisly scene is major disgust and not a whole lot of tolerance. A person can only muster courage to cause so much carnage and blood if he is desensitized to it or if it were glorified in his culture.