I never thought about it before but Full Metal Jacket is kind of retrograde the way it portrays the guy who blasted his CO as a sobbing incompetent moron. In reality there was a lot of resistance and direct murder of COs by GIs during the Vietnam War, but it wasn't done by antisocial mouth-breathing idiots but principled resistors.
Sir, No Sir is a great documentary about GI anti-war resistance whose thesis is that it was actually the internal resistance to continuing the war at all levels from infantry to intelligence that forced US withdrawal.