While I haven't played it, I feel like I know enough about it to know that despite Dutch being a sociopathic maniac, he's almost like a cult leader in a way. He's swayed these people with past favorable actions and charisma to the point where they are nearly brainwashed at this point. That's why Arthur struggles so much with defying Dutch, even though to the player is seems like an easy decision.
Correct me if I have this wrong, of course.
you're 100% correct. Arthur and John were raised by him so he's like a father to them and on top of that he's fairly well read, eloquent, and charismatic. He's fostering a cult of personality and while he is obviously full of shit when viewed from the outside and with the knowledge of how RDR1 goes down, from the inside many of his gang likely don't see it that way for a number of reasons which we don't really see in-game. The thing is, we enter the story from the beginning of the 'Decline', as it were, and we don't have the benefit of seeing the gang's past successes up until then, and from the characters reactions to how the Blackwater job went down many of them were upset about Dutch 'killing that woman' as though it was outside of the norm for him to do so, so we can also make an assumption that the maniacal tendencies that Dutch eventually succumbed to were new even to members of his gang that had been with him for decades.
Not to mention Hosea was not only the brains of the group but a calmer voice of reason to keep Dutch in line, and when that influence was removed Dutch went further off the rails in an obvious manner.
with that in mind characterizing Dutch as an 'obvious unlikeable sociopath' and Arthur as a 'Stockholm syndrome pansy' seems like a gross oversimplification, in my opinion. Not that the story of RDR2 was a masterpiece or anything, frankly I had my fun with the game but I think I much preferred RDR1's story and I even think RDR1 tackled the themes of civilization intruding on the Wild West and modern living suffocating those who didn't want to or couldn't adapt to it and all that better than RDR2 did in many respects.