I support guns for the same reason they're protected by the Constitution. Not for the sake of personal protection from thieves, attackers, or foreign nations, but for the sake of protection from a corrupt government. It has been said to the point of being a cliche, but people should not be afraid of their government, the government should be afraid of their people. The right to own guns is an assurance that no matter what happens, no matter how corrupt or detached the government gets from the people it governs, as long as the people have the right to bear arms, they will have some say in that government, if only through revolt.
Of course, the spirit of that interpretation has long been subverted.