Soldiers have been firing - or swording - on their own since the beginning of militaries, in fact, that's usually who they were used against, including here in the 1770s and 1860s, etc. To think they'll disobey orders because cousin Jeb is standing over there and Trailer Park Tom is over that aways is silly. Just ask a cop or any other agent sent to apprehend a fellow citizen...
Ruby Ridge, Waco, pew pew!