I'm in agreement with most of the other points you've made. I think the only rationale that applies mostly to the U.S. is the one of referring to the U.S. as America. Although I know what is meant when Americans say they're from America, to me personally it sounds a bit strange, considering America could also be used as a synonym for the Americas, which would include North, Central, and South America. When talking about the United States of America, I generally prefer to use such terms as the U.S., USA, US of A, or just "the States." American seems fine to me, but America to refer to the just the U.S. comes off a bit strange.
So you agree ...
except ...........
Which means you don't agree.
I'm not not "yelling" this, really. Agree or don't agree with me, that's OK. But it sounds as though you want it both ways, or as though you are making an effort not to sound unpleasant or hostile - which is lovely.
I suppose I could understand and not take offense if this term "Unitedstatesian" was used only in a language other than English. After all, it's not a word in English, and it sounds like a rock rolling downhill.
I know "Italy" is not the proper name for Italia, Italy is what Americans call the country Italia. If I could speak Italian well enough to speak it, I would say Italia when speaking in Italian. If an Italian speaks English to me I don't expect them to say Italy instead of Italia, it seems like an absurd imposition. I happen to think Americans, a theoretically multi-cultural country, should use the proper names for all countries. It's not that hard.
I think a country gets to decide on the word for its own name in its native language, and by extension, the appellation for its' citizens.
Do you, as a Canadian citizen, wish to called an American?
As a native English-speaker, knowing the grammatical difference between "an American" and "The Americas?"
Do you live in America or Canada? Do you refer to yourself as an American in conversation? Really? If I go to Montreal or Quebec or Winnipeg and refer to the locals as "Americans" it would be understood and accepted?
I truly believe that many, if not most Americans have no idea that this is a topic of conversation anywhere in the world, and if I tried to explain it to them many of them would think I was making this up.
I think it's fine if other citizens of The Americas refer to themselves as Americans, though I think it may be confusing on occasion.
I really would have thought that citizens of other countries would have been offended if I referred to them as Americans rather than the name of their own country.
I would worry that it sounded as though I was minimizing their own country's uniqueness and singularity, and was reducing them to a small part of a large group.
What really bothers me is the notion that another person thinks they can deny me my name in my own language.