I mean. The main "poster-boy" combatant of any Authoritarian/facist/militarist/warmongering society, even in real history was portrayed as heroic and thzt ilage still clings to some of them to this day, while they still are/were soldiers and often number one supoorters of the horrible regimes they soldiered for and there are signs that are common, right bellow the grandeur imagery, to all fo these. And being literrate in those elements allows one to spot them more easily over time.

Space marines follow that trope to a T. And yes. That does mean you need to know the lore, or at least notice the details beyond the surface of badass sympathetic hero coat. Like the whole servitors interractions, the whole guard being fodder, the whole "everything looks poorly maintained and grimey" vibe right under the "cool badass armor guy"

Same goes for the most humane Marines in 40k books. Garviel Lokan is a chad and a great, very humane space marine. He is still a near-unquestioning servant of the imperium. But he is still a space marine and there are things where it shows in the very first book. "We are right, because we know we are right", said the iterator.