You make good points, except that the experts in our armed forces seem to think that full auto has benefits justifying arming most soldiers with such rifles.
If you had to cross a field with hostile shooters nearby, would you rather your pals have machine guns or semi-autos to provide supressing fire?
Machine guns to provide suppressing fire, semi-autos to take out the shooters.
Besides, if the Second Civil War ever starts, I doubt the military would be on the side of whatever fascist democrat was dumb enough to rip apart the Second Amendment.