*Let me shed some light on the CCP's propaganda, and explain a bit why your statements might meet a deaf ear.*
I present this to showcase the rationale behind many pro-China netizens living in China (both ethnic Chinese and non-Chinese).
Note that I could not give detailed references, because I am not a professional political scientists or historian, and I do not keep such records. Hopefully it opens a window for more directed Google search.
> CCP is blatantly overstepping their rights in those regions.
Legally, CCP inherent the rights of KMT, which inherent Qing Dynasty, who has sovereign rights in most conversational lands. The KMT inherentance from Qing, was sealed by certain legal documents following the contemporary international laws and conventions at the time. The KMT to CCP overturn is of course not legally sealed, but in general it's reasonable to assume the transition is legal from an international laws' perspective, for example: https://en.wikipedia.org/wiki/Westphalian_sovereignty (note that I did not read this concept deeply, I was just getting 2nd hand information elsewhere, so I could be wrong).
> CCP is an invader, not the rightful ruler.
This would just be treated as "western propaganda".
In CCP's theory framework, CCP is the servant of people (much like US police, and for that we all know how much truth is actually in the deeds). And for the vast majority of people, because CCP controls a significant portion of the national economy, and they can use those resources to provide social well fare to the poorest. So it's reasonable to claim that CCP practiced this ideology, and "CCP as people's servant" is quite well received. I would say it is about as popular as "democracy is good" in US. (Note that I did not claim one is more true than the other, it was just my observation of people's ideas).
So with that framework, the statement intermediately falls apart. (And we can all assume that people don't investigate, they just consume propaganda. I think this statement is universal so far in human history).
> They're starting the same incrementalism over the 9-dashed-line, and even Taiwan.
These are all based on some historical evidences. Which at the time does not very well map into the modern cultural and political concepts. But again, China shaped east Asia's cultural and political heritage for more than 1000 years, you can see that there is some form of legitimacy in the mind of the people at the region.
> Just because a nation invades, forcibly relocates, 'reeducates', and culturally overwhelms and erased a people does not make them the legitimate ruler, nor does it make foreign nations working to support the remaining rightful owners "interfering in the internal affairs" (&yes, I see that this also applies to the USA over Native American rights).
Invasion was labeled liberation. If you look at the economy and production level of Tibet before CCP's invasion, certainly CCP have brought modern production means and built a much better economy in Tibet. As for how much was lost in the process, I don't see much. Tibetan still lives a quite traditional way. They certainly are not bothered by the CCP's presence. As obviously, to maintain CCP's ruling, Tibetan have been treated much better than the mass majority elsewhere. Even their lands were largely left for their own use, because immigrants from inland do not perform farming work, and mostly live in concentrated urban area.
"forcibly relocates", AFAIK, rarely happened. I do know personally some Uygurs in my college where they were treated as "above law and order in the university" because they are minorities (they are usually left unmolested when involved in some fights between youngsters, for example). They never complained to me about relocation. But I have no Tibetan acquaintance. Of course, it could be that CCP have combined good treatment and harsh policy to silence such complaints. But I have not seen such evidence. And you can be sure that the mass majority would have no such evidence either.
"culturally overwhelms", well, that certainly did not happen from what I can see... As I said before, Tibetan and Uygurs, and many other minorities still live their own ways. They certainly are affected. For example, they are like other peasant workers, need to leave their homeland to work in east and south region, and often get to live a different culture. But they are not losing their heritage when they retreat to their own domains. For this I have first-hand experience from my travelling in China.
"erased a people", minorities, like in US, have their population growing faster than Han people. Minorities are not subject to the same harsh one child policy as Han people. For example, I was nearly died if not my mother escaped a forced abortion by fleeing from the city to the rural area in my home town. Such things were never practiced on minorities. Although, officially, CCP never had a forced abortion either, but you can see the acolytes exerting their own cleverness here...
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The rest of statements are more vague and general statements. It usually were brushed off from the natural inclination towards China's national interests. Everyone, probably except Tibetans and Uygurs, knows that the national security would be in jeopardy if Tibet or Xinjiang becomes independent countries; and the situation also applies to 9-dashed lines and Taiwan.