> it would be done under the authority of the gun, not under the authority of the Constitution

It would be done under the authority of "the People" - the same authority through which the US Constitution was enacted (or so the logic goes)

Note that the Constitution does not "grant" a right to arms, but recognizes a pre-existing right. Take away the Constitution, and the right remains.

Same difference (a group of people armed with guns are going to have a better time issuing edicts than a group of unarmed people...).

The point is that threatening to take up arms against the government is an ironic companion to constitutional fervor.

I see where you're coming from, but I don't agree. The Constitution specifically protects the people's ability to maintain the force necessary to be a credible threat. If not to maintain the threat of armed rebellion, what purpose would it serve?

Obviously actually engaging in insurrection against a constitutional government would not be constitutional. Anyone taking arms against the government would presumably believe that that government was not operating within the confines the Constitution provides; the act of insurrection would be seen by them as a remedy to an unconstitutional government and therefore neither party would be subject to it.