So we should place all our trust in our future in the hands of the police and military? If circumstances should change such that the government becomes corrupt to the point of needing overthrowing, should the people have no means to exercise their strength? I don't trust the government to be the only institution with power. They're untrustworthy enough as things stand.
Also, it's not like making a gun is really that complicated. With a bit of internet reading and some determination, anyone could make a gun in the league of the muskets of old. A legitimate artisan in the craft of gun making could pretty easily make a quality handgun with common materials. It's really easier than drugs since you can do it in a dark and hidden basement that's quite hostile to growing things, and all things are completely portable. Of course, the black market would thrive. Criminals would happily pay for guns, and as long as there are drugs to sell (which many anti-gun people use...) and things to steal (this one's kinda unavoidable), criminals will have money. The only way law enforcement could possibly stop an arms market would be by totally invading the privacy of everyone. Really, in order to stop people from simply hiding guns in their homes, the government would have to conduct random, highly invasive searches which I'm sure anyone who even remotely believes in the ideas behind the USA would be opposed to.
I'm also pretty sure it would be unconstitutional; the 2nd amendment isn't that narrow. Of course, the Constitution seems to be a detail to most people so I won't harp on it.
Lastly, there's no reason. Murderers will murder with whatever tools they have at their disposal. The guns are just a tool. Banning the guns doesn't fix the problem. Do you think the shootings you hear about on the news would all just go away if guns disappeared from the world? Was the world a peaceful place before guns were invented? I've heard that places like ancient Rome were far more violent than even the worst neighborhoods in modern America, and the best killing tools they had were swords. It would be the same way here if we eliminated the guns. Absolutely nothing would change. Well, I suppose muggers would have an easier time since their random victims would be assured to not have such a means of defense, and if the mugger had an illegal gun, his job is really easy. I don't see the gain here.
I have yet to see a single statistic suggesting that decreased gun ownership leads to decreased crime. I'm calling shenanagans, and I would go so far as to claim that it's a lie as ridiculous as video games causing violent crimes. It makes sense to some people, but there's no evidence to support the claim. The lack of evidence can only lead to the assumption that the premise is false, no matter how popular the premise is.