If it was, even in principle, possible to fully control guns then there might, within the context of these criminals, be some justification to the argument under present circumstances. Only, so long as ACE hardware exist, I can have a gun. Even a fully automatic one with over a thousand rounds. Perhaps not as accurate, but as deadly as a continuous shotgun blast.
If guns are outright outlawed then the manufacture and distribution of guns will take on the same character as the drug trade. The more severe the penalty for getting caught, the more incentive it creates to kill to defend this enterprise, and you can forget any notion that the general population is anything but a pig shoot if it serves their purposes.
Even in the best case scenario, where criminals are not the issue at all, can you guarantee that there will never be any point in history when people have to defend yourself from being killed legally? In fact it was just recently signed into law that assassinations of American citizens is legal. Just a few years ago that would have seemed so absurd as to be laughable, yet here we are. Certainly it's something that should be dealt with in the legal system, rather than guns. It simply doesn't even come close to warranting that kind of response at this time, but what assurances can you give that it never will at any point in the distant future?
Simply taking the drug trade away from the criminals, by giving it legitimate regulated channels, will not only save millions more lives (yes millions), it would save even more millions from ruined lives for getting caught doing no more than many of our elected presidents have done in their youth. Even an entirely successful outlawing of all guns would compare like a grain of sand to the beach. In fact drug laws/penalties are what makes the gun statistics look so awful, while insane asshats, like this latest shooter, gets all the press for justifying making things worse.
Laws toughened beyond some point makes those partaking in the activity more deadly. Nothing can EVER be made to go away simply on the grounds of passing a law against it. The law must balance the risk ratio so as to discourage certain things without increasing the risk imposed on the rest of us when we come in contact with those partaking in such behaviors. The gun control lobby doesn't seem to care anything about any such balance. I can't count the number of times I would have likely been shot if the law made the penalty for the things I witnesses too high. Your not even safe hiking national forest, for reasons unrelated to any gun law.