Thank you for pointing that out. From the outside, many countries look like homogeneous collections of people, but the vast majority are not. China's ethnic tensions are not limited to Tibet, and many minorities feel their cultural identity is being threatened. The Chinese government isn't as self-serving and evil as they are often portrayed in the media. Once you actually learn (SO out of vogue, I know) about things there, it becomes pretty clear that their motives are, yes, to preserve central government power, because the alternative isn't just letting everybody be happy and free, it's quite the opposite: Outright civil war in a nuclear-armed and global economic pillar. It would be hell for the billion plus people within its borders, and very bad for everyone else on Earth.

I think it's important to note that it's the natural tendency of any nation to head down that path regardless of its particular system of governance, ideology or economy. Some get there faster than others, but without constant, conscious and vigilant course corrections by the people as a whole, they'll get there sooner or later.