The citizenry wouldn't have to fight the U.S. military. Some of the strongest supporters of the 2cd Amendment and the Constitution in general are in the military. I firmly believe the military would turn on the government before they'd turn wholesale against the American people.
This is the part of the argument advanced by gun advocates that I just don't get: the risk/reward equation.
The 2nd amendment is intended to enable the citizenry to protect itself against invasion or, for lack of a better term, "political upheaval" Am I correct?
The risk is that the availability of guns will lead to their use for purposes not intended by the 2nd amendment: domestic violence, mass shootings, etc.
Given that the US hasn't been invaded since the war of 1812 and that the various terrorist events that have occurred weren't stopped by an armed citizenry, is the reward worth the risk?