Guns won us our freedom from the tyrannical King George,
Historical revisionism. A more accurate description would be that guns won the American populace the switch from the tyrannical rule of the British aristocracy (which was, ironically, not "tyrannical" like other European states were due to a constitutional, rather than absolutist, tradition) to the tyrannical rule of the American aristocracy.
and if necessary they'll win us our freedom from a potentially tyrannical Washington, D.C.
Completely unrealistic unless the central government is a puppet regime installed by foreign invaders, thus inspiring a significant portion of the populace to take up a guerrilla campaign which would necessarily have substantial foreign backing in order to succeed anyway. "Home-grown" authoritarianism would be immensely popular; anything more than a saboteur underground resistance movement is inconsistent with an authoritarian regime even attaining power in the first place.
Less important issues are the near-future possibility of replacing human soldiers with robotic drones (which, with extreme mechanization of industry, could be mass produced with ease), and the mildly paranoid tendencies people frequently display when advancing such arguments.
The only conceivable reason for the government to ban guns is as prelude to stripping us of our fundamental rights, which they know they would never dare do as long as we have an armed citizenry.
Or because it is believed that decreasing availability of weaponry will decrease levels of violence (which is consistent with the psychological literature). And then, again, a mildly paranoid fringe armed with pistols and probably already in pro-government fascist paramilitaries spending their time beating up/abducting dissidents anyway will not effect the policies of an actual authoritarian regime in any way.
Believe it or not the constitution, what it says and how it's interpreted is a big deal to a lot of Americans.
Which is ironic, considering the problem many individuals, including liberal philosophers amongst the "founding father" crowd, saw from the tyranny of the past. For the present generation to fanatically devote itself to the traditions of past generations, basing its identity and attitudes around them, destroys its own sovereign character and invariably leads to undesirable stagnation.
Deferring to an old sacred document for moral guidance is illogical regardless. Was slavery good when the Constitution protected the institution? This is the only consistent conclusion with a "support everything in the Constitution because it's in the Constitution" attitude.
