Is there a specific reason why Black Sun Troopers all wear gas masks?
Dehumanizing the enemy. - This is important, so that you can easily kill off any one of them and still be “the good guy”.
If you would give them a face, feelings, family, then you would have the problem that you more often than not murder some fellow humans.
Dehumanizing the enemy is the basic way of making it easy to kill them.