Why a libertarian might favor gun control

I hold opinions, as I've expressed here, that are generally quite libertarian. But I believe in very strict gun control, probably stricter than most who do not share my libertarianism would have. How do I justify this?

The libertarian credo is that everything should be legal unless it harms another person. Guns have no purpose except to kill, and so I cannot see any reason that a normal person could have a use for a gun. I would restrict gun ownership to two groups of people: the police and the military. Both of these have a need to be able to kill as part of their official duty, and so they need guns.

Some people say, "When guns are illegal, only outlaws will have guns." Of course; by definition, because those with guns will be outlaws, and mere possession could be an excuse for their arrest and confiscation of the guns. So criminals could be deprived of their guns before they could use them to do anything harmful. Why would an honest person have anything to fear?

Again, some people say, "Guns don't kill people. People kill people." Certainly true -- I've never seen a gun go off and kill someone without someone touching it. But guns make it easier for people to kill people. If you have to use your own personal strength, or at least a knife, and you have to get to a position of physical contact with a victim, you'll have a harder time accomplishing this deed.

So this is my case for gun control, no matter how much of a libertarian I am.