Raul gives us a good reason for why people like the Legion/don't rebel: because the Legion plays cop. I'm also of the fanon that the Legion leaves most cities and towns alone; their army consists of Tribals Caesar can warp and forge from the ground up, while Urbanites, if they survive the 'anti-raider cleansing', are basically autonomous; they might encourage recruitment, but so long as most of their women and children are left alone and their chiefs left in power, you get a mutually beneficial relationship.
Granted, if a legionnaire snatches a woman from a town or a centurion press-gangs your men into the army, you're not going to win that fight, but in that regard it's little different from when the raiders and gangs ruled. That's how shit the four-state commonwealth apparently was.
The main points of contention comes from the whole slavery thing, the ingrained misogyny seen on the frontlines, and the stagnation brought about by Caesar's own world-view. Which is totally okay, because, again, if they didn't want to make the Legion be so laughably evil, they should had at least churned out a lot of supplementary/semi-canon stuff to negate the lack of hard coded stuff.