I would like to raise the point that killing with a gun is probably a lot easier than killing any other way. With a gun you just pull a trigger. Bang. Dead. Very clean (in a morbid sense). Now imagine killing someone with a knife. You have to physically grab hold of someone and repeatedly stab him in the chest. That, in my opinion, turns around the whole "they would have found another way anyway" theory. And if it isn't a knife, how creative do you think people will get? Use broken glass? Get a baseball bat? Set traps? You don't do that sort of shit in a reflex, is all I'm saying.
Psychologically speaking, shooting a gun has a lot, LOT lower threshold. And not just for the maniacs out there. If you have a gun for protection and you're suddenly in a very threatening situation, your survival instincts might take hold of you completely and there's no telling what you'll do.
I don't have any stats on this, but I bet deterministic murderers like that sniper last year are responsible only for a very small percentage of the actual incidents. Aren't most gun fights more like ... uhh some gang and some other gang and everyone is like "shit shit shit", people draw guns and some of them die? Or, like, a robbery gone bad? Or some neighbour dispute and one of them draws a gun? Whatever. I'm just pulling up some random scenarios from Cops. But that's still probably the sort of thing we're talking about. Not the maniac laughter type of killing where any means of killing would be pursued?
Anyway, why not ban guns AND try to fix whatever motivates people to kill? Kill one bird with two stones, so to speak.
Beh, it's late now. I should be playing with that sound board.
