Yeah, and growing up I heard the exact same talking points about the Confederacy. How states should have the right to decide whether they want to be in a union or not, how ending slavery was the real slavery, how it was authoritarian for a central body to tell us who we couldn't enslave, how Southern culture was lost by the North imposing it's ways on us. Just another nation-state trying to control the little guy. I've heard it all before.

If there is some rationale that can actually justify bemoaning the lost cause of the Tibetan slaver theocrats, it's probably for the best that I'm not clever enough to see it, because I'd have used it to justify the beliefs I was raised with and might not have ever become a leftist in the first place.

It's completely absurd to speak of "self-determination," especially "socioeconomic self-determination" regarding a literal slave theocracy. What, you mean the "self determination" of the theocrats? Because the serfs didn't have self-determination to lose in the first place. Again, there's no shortage of people in the South who would bemoan the "carpetbaggers" and the loss of Southern "socioeconomic self-determination" (though they might use different terms), completely glossing over the fact that slaves had zero socioeconomic self-determination under their system.

You are the one who's adopting a statist perspective by treating the serfs and their lords as one entity with unified interests, when if you look at if from a class perspective, they had diametrically opposed interests, with the interests of the serfs being in line with the interests of the Chinese people and the revolutionaries. Which is why so many of them supported them (in spite of the slaver theocrats' attempts at religious indoctrination).

Of course, another reason is their shared history. Tibet had been part of China for hundreds of years, which is why it's still claimed as part of China by the ROC. During the brief period of chaos following the collapse of the Qing, it emerged alongside countless other warlord states that were opposed by both the nationalists and communists, as well as anyone with half a brain who could see that the division is exactly what allowed them to be invaded by the Japanese despite them being a much smaller foe. In fact, during WWII, the US military produced a film that states that point explicitly.

China would have been wrong to have not freed the Tibetan serfs. Perhaps that liberation was imperfect or incomplete, just as the liberation of slaves in the US was, but it was still a step in the right direction that massively improved the quality of life for the vast majority of Tibetans.