Apples and oranges, Dave, apples and oranges. We're not talking about homicide rates in urban centers, household violence in trailer parks, not about gang wars, not about organized crime, not the Uma Bomber or armed robbery and theft. All the above are relatively insulated against gun control, I agree.
Our scenario is "nutcase doesn't lke Mondays and proceeds to massacre a few people wantonly chosen by him or just unlucky enough to be around". Mostly, those people don't build explosive booby traps in the solitude of their home for months on end nor do they book flights to Syria to buy derelict Sturmgewehre because gun trade has ended in the US. They grab the gun in close proximity or buy it at the gun shop around the corner. Tougher gun laws won't prevent all these tragedies but wouldn't they even be justified if they prevented just one? Philosophical, not political question.
And Dave, for a man as smart as you, it pains me to see you taking up the populist "blame the media!"-argument. Based on that argument, we should ban all literature and films on the Holocaust, caterpillar Auschwitz into the ground and just pretend it never happened, life goes on after all except for a couple of unlucky jews. Otherwise we risk repetiton genocides. Evil goes away if you just ignore it.