I’m sure the USMC has their better moments, and attracts some truly dedicated, courageous young people to the profession of protecting our country. On the other hand they also take a lot of confused young people looking for a purpose in life and turn them into remorseless killers.
I had a friend years ago whose brother enlisted in the Marines, who I’d known as a rather aimless sad sack. I hung out with him when he was on leave after being in for a year, and he’d gone from pudgy to ripped, but after he got outside a few drinks all he wanted to talk about is how he and his buddies would go on leave in Virginia Beach and look for fights. Their favorite thing to do was beat up Navy sailors.
The Marines put a lot of energy into their ideas of Duty and Honor. But make no mistake — it is the military, and arguably the most hardcore of the US Military services. Their highest value in real world is to create a fighting force that kills enthusiastically on command with no qualms whatsoever.
If anything, Avatar presents a version of the USMC that’s better than the reality — it has a Marine with actual moral qualms about immoral orders. That’s exactly the sort of thing the USMC fears most in their soldiers.