> From what I understand it is as often a problem with translation as it a clear political standpoint.
In principle, yes, and I do think this is an underappreciated issue which, if understood better, could have avoided several needless heated arguments in general.
However... Where does your understanding come from? It runs contrary to my experience from living in the region.
IME, "Mainland China" is one of the least loaded and ambiguous terms, and tend to refer to "the literal mainland of the PRC" (that is, sans Macau and Hong Kong, and definitely Taiwan).
> When you say "I am from mainland China", there is a good chance that you do see Taiwan as a 'rogue province' and may support its 'inevitable' reunification by any means, including force. That latter sense is the one that is highly political and irks many people.
While technically, yes, but it could equally (and probably more often in practice?) be used by people who recognize the independence of Taiwan and do not want to force a "reunification".
"China" (and even more so "Chinese") is more open for being problematic as it can imply the citizens, ethnicity, cultural heritage, the CCP, the PRC nation-state as such, etc... Being more specific removes room for misinterpretation, willful or not.
This is my perspective from living in the region for a couple of years. Though I wouldn't say I've knowingly interacted with more than a small handful of "pro-unifiers".