Think about this - the marines, and the other branches, have a majority of folks of good character, good character based on generationally engrained Christian values and beliefs. This is why they won’t follow the order to fire on civilians.
However, why do you think that the left has been adamant about homosexualizing the military and punishing/purging those who won’t accept it as “normal”?
You get a twofer - you purge the Christians out, you purge those of good character out, and you fill the military with those who are already predisposed to a depraved mindset.