I know it wont stop it, but it will lower their chances of obtaining one. Public area's will no longer be able to sell them, and the buyer will have to search harder, longer, to find his gun. Sure, the attacker can find a different weapon, but guns are probably the easiest weapon to kill someone with, without knowledge that "you" did it.
I dont know, its just a personal view. With gun stores being as common as a wal-mart, its just annoying to me.
Edit: We arent blaming guns, just their availability. Almost anyone can purchase a gun legally, which is our problem.
Kinda like how hard it is to buy drugs? Or how about how hard it was to obtain alcohol during the Prohibition era?