Red Dead Redemption Explained: What Does The Ending Really Mean?

This is true not only of Mexicans in RDR, who are forced to choose between two egotistical leaders in Allende and Reyes, but also of Marston, who has to conform to the demands of Ross and the BOI.

Marshal Johnson of Armadillo is also the oppressed, even though he is the sheriff - he has to allow criminals to drink in the saloon, because they don't rob people during that time.

The BOI don't have to bow down to anybody - they are aware that they are considered the bad guys, but someone has to set the rules for the rest to abide by.

Following their reasoning, it's better them than somebody else.