I was always confused about the necessity of selling firearms. I mean, the self defense rationale doesn't really work if they're illegal for use altogether (save law enforcement).
But right now, guns are just so ingrained in American culture that getting rid of them altogether will be impossible. I think the best we can do is regulate it.
And yes, even if guns are gone, people will still kill each other. However, guns make the process insanely simple and impersonal, as IT'S A LION! pointed out. I mean, it'd be hard to kill over 30 with stabbings. Do you ever hear of mass stabbings? I haven't (but I guess it's possible, someone please correct me if there was a serial stabbing case).