It's literally on their border and the history is akin to if The South established its own nation state in Cuba after the Civil War and China became its ally.

At least admit the double standard. I don't mind realpolitik but it's so tedious when it's not plainly stated and there's this veneer of civility.

Yes, the US is allowed to do whatever it wants to in South America. No, other nation states don't have a sphere of geographic influence if the US doesn't want them to.

Taiwan has been self governing for longer than almost everyone that lives there has been alive. It's also a vibrant democracy.

If you care about democracy and human rights, it's morally reprehensible NOT to support Taiwan. We can debate the ethics of intervening in strongman dictatorships like Venezuela, Cuba, or Iran, but Taiwan is clear.