Sorry, "who" considers themselves a nation? The Han Chinese living on the island of Taiwan. No. I don't think you'll find that opinion to be very popular nor very defensible.

Also, an increasingly large group of people there consider themselves Taiwanese first, Chinese second (or not even Chinese at all). Support for unification is very, very low. It is in fact a popular opinion to favour independence or to believe they are already independent (Huadu).
I know you want to say history doesn't matter, but it does. You can keep saying it, but it won't make it true.
Strawman argument, I never claimed anything of the sort. History matters up to a point. The right to self-determination also matters however.
The actions of the US regarding black people are abhorrent. They also matter, because their effects are felt by people alive today. But those events are in a wildly different category than matters regarding territorial claims.
For example, I think the zionist claim towards Israel is imo basically bunk; maybe some ancestors have lived in that area 2000 years ago, but in my opinion that does not trump the rights of people who live there today, and whose parents and grandparents lived there. Basically, if you're forcing someone to move somewhere else, or are forcibly assimilating them into your country without any form of proper democratic input, I think it's wrong. I think that the rights of people who live in Taiwan trump some claim based on territorial borders from over a century ago. Unless the people there vote to become a part of the PRC, the PRC has no right to annex them. Similarly, the old ROC claim to mainland China is equally bunk. I don't give a hoot about what people 100 years ago wanted to be a part of, I care about what people want today.
And just to clear this up in case you were wondering: I am not an American.