I think it's a moot point, whether or not individuals can keep guns. I see no reason not to restrict gun ownership to bolt action rifles, 3 shot shotguns, and revolvers. That certainly doesn't violate the Constitution. The idea that you are going to fight off the government is ludicrous, on its face, so we have to rely on other ways to keep the government from becoming tyrannical.
Frankly, I'm more worried about corporate control of the government and the effects of Citizens United. The next tyranny might not be a militaristic one that you fight with bullets. Maybe it will be based solely on economics and credit control? Don't play along and you get removed from the game. Maybe it will be social? A Facebook tyranny? "Why do you have this distasteful statement in your status, Mr. Citizen? We may have to remove you and of course, Mr. Employer won't hire you if you don't have a profile he can look at, or a good credit rating. Oh, and you can forget about buying a house." What matters individuality when you have been swallowed up in the herd?
Also, what worries me more is the corporatization of our military; Private enterprise taking over military functions. An army of citizens might not fire on those who they consider their own brethren (especially if the people revolt over issues shared by military members, as we saw in Egypt), but would an international, private military force have any qualms about taking orders from their employer? The Romans started hiring out their military duties. Look what happened to them? Perhaps those sitting on their basement arsenals are looking in the wrong direction while their freedoms erode away right under their noses? While they look out for the commie tank to come over the hill, their freedoms are losing their potency, one by one, as the freedom of individuality disappears.