As I just said to mentha: The Longcoats are military men, essentially. They can justify a hell of a lot by saying, "I'm just following orders; I'm just doing my job; my family has to eat; I'm keeping the roads safe; I don't care about politics" and so on. Beyond that, though, I figure Azkadellia and her inner circle have done a lot to twist the facts, so that the vast majority of people aren't aware of the full extent of what's going on there. She's probably convinced many of the Longcoats that she's the rightful ruler, the more fit ruler, a more generous employer, etc. The tin men were remaining loyal to the old, unfit, "corrupt" regime, and thus had to be removed for the "security" of the O.Z.
Basically, I find it much easier to believe that your average Longcoat fell victim to propaganda and/or turned a blind eye to things in order to justify their actions than I do the notion that hundreds of people willfully chose to follow an evil leader because they liked exerting power over other people. (Granted, I'm sure there were some of the latter, and those are likely the ones who gained rank...) It's also possible that what started out as "distasteful bit necessary actions to maintain safety and order in the O.Z." turned into standard behavior over the years as the Longcoats got used to their actions and positions.
Ooh, I like that. Maybe the other Longcoats just thought Cain was a resistance member, and Zero was the only one who knew he'd been a tin man as well. :D I really wonder about the past history between Cain and Zero, because there seems to be some serious animosity on Zero's part; Cain's not just another ex-cop that he stuffed in an iron suit, yanno? Also, I'm really curious what made General Lonot defect.