As a retiree from the military, I would say a lot has to do with the putting on a uniform and swearing an oath to visit death and destruction on the enemies of Her Majesty (as ordered), and being trained in tactics and the use of arms for that very purpose.
It’s like it’s OK for a Vancouver Canuck to bodycheck a Montreal Canadien on the ice during play in a Montreal-Vancouver game. He cannot, however, do the same to a Habs fan in the stands (no matter how hard he is cheering).