Tibetan history is actually far more complicated than that, but few saying "Free Tibet" seem to know that. Mind you, I'm not saying that China's behavior is appropriate or that the Tibetans don't have a right to independence, but it would be nice, for a change, if people actually gave a damn about the truth and then formulated their opinions (don't even get me started on the Israeli-Palestinian situation). Failing that -- after all, it's easy to rush to judgment -- we should at least be willing to consider that our views may be wrong or simplistic.
So just for an interesting bit of contrast, here's an interesting report about the Dalai Lama suppressing freedom of worship. I'm not saying I know that this information is true or an accurate representation. I'm saying that it's worth knowing if you care about the situation in Tibet.