Anyone who has ever, even or perhaps especially when alone in the house, posed with a gun in front of a mirror should seriously consider their mental fitness to own lethal weaponry. To any such people, I ask: What facial expression did you try to adopt? Stern? Resolute? Noble? Or just hard? What childish fantasy did you conjure up, with yourself as hero, saving the world or perhaps just felling the baddies in a shower of lead?
I'd suggest that there is a fundamental difference between the psyches of the gun murderer and the suicide bomber. The suicide bomber requires anonymity up to the moment of detonation in which his own instant oblivion is assured. The gun murderer on the other hand actively desires the thrill of firing his gun, over and over, at real people. He does it for his own sick pleasure, whatever lies he might tell himself about serving a cause.