I agree with Don. It's what they call the "veil of ignorance". Say you were in some interdimensional area and you knew that in a few moments you were going to enter the real world and be put in a situation where a certain number of people were going to threaten your life. You can choose between two worlds to enter, both with this same situation. Do you enter the one where you are allowed to own and carry guns (and for all you know are an expert) or one where you aren't (and might be a 5'2" woman about to be attacked by two large men)? Frankly, if you chose to enter a world where you wouldn't have a gun in that situation you're either a fool or a martyr.

Of course there are other scenarios. I'm sure a few people bystanders have been shot in ways they could never have foreseen. But it boils down to the social contract like Don said.

Fireworks are similar to my mind. Every 4th of july hundreds of people injure or maim themselves setting of fireworks. So the government tries to outlaw everything but sparklers (and have unfortunately succeeded). But really it should be left up to the people to decide. Same thing with alcohol. Kills a lot of people. But it's the individuals choice.