The American people can wipe out the parties at their leisure, they have chosen not to. Throughout American history, our parties have changed numerous times, some disappear, some rise, some evolve, and that isn't going to stop.
Americans get to choose. If they choose to be brainwashed as you call it, then that's their volition. If America collapses, it will be the responsibility of the people that they didn't use their voice while they had it.
The Chinese do not get to choose anything. Every time they try - and they have tried - they get violently put down by their own government. In China, nothing like the Occupy movement would ever be tolerated at all, those people would not be allowed to squat on park property and protest, they would not be allowed to march, they would not be allowed to do even a fraction of what they got away with here in the states, and it sure as hell wouldn't all be filmed and put on YouTube for everybody to see.
The various movements of the 1960s and 1970s would have been completely impossible in China. Try holding a rally for free unionization rights in China some time, see how that goes.
Try openly and expressively declaring your religious beliefs. See how much they love that.