True, outlawing all guns won't stop gun violence everywhere, but it will drastically reduce it. If you can't legally obtain a gun at all, then you'll be less inclined to own one, and less inclined to use one. With current gun laws, a cop can find a gun on you and you'll be let off the hook if you have a permit. That's fine; that's how the law works. But then you use the gun to kill someone; well, doesn't that suck? Sure, there's always the possibility that some nutjob will pop out of nowhere and shoot at you. But does that mean anything, really? Simply owning a gun won't mean you'll be strapped with two six-shooters and instantly pop a cap in the guy. You'll probably get gunned down regardless, because that guy had easy access to a gun.
My view is essentially this: It's possible to have a utopian society where everyone owns a gun and yet is responsible enough only to use them for, say, target practice. But we don't live in that society. The way humans are right now, we don't really deserve to have guns. When people outright stop shooting others because they insulted them, or their beliefs are different, or their actions were misinterpreted, or they were in the wrong place at the wrong time, then we can safely have guns in our society. But that's just not the case.