Here is the whole quote:
The film glorifies the Confederacy as if they were a bunch of highly principled martyrs hunkered down in holy glory instead of an entitled mob of human-trafficking murderers, rapists and traitors trying to destroy the United States
This doesn't check out for me. The way I understand "hunker down" is something like (physically) "squat". Or more metaphorically, stay in ambush, wait for something to happen in some place.
I cannot figure out how that lowly posture could rhyme with glory or martyrdom, or any cultural reference it may hint to.