You're being disingenuous. Look at the articles mentioned in the quote.
"Taiwan Relations Act, the three U.S.-China Joint Communiques, and the Six Assurances". In particular: "The United States would not formally recognize Chinese sovereignty over Taiwan"[1].
So the US supports a "One China policy", "does not support Taiwanese independence" and "does not formally recognize Chinese sovereignty over Taiwan." And it will supply Taiwan with weapons to defend itself, giving defacto independence. And, as you quote, the US opposed any unilateral changes to the status quo.
Confusing? Yes. Yet you're misleading people with your post, frankly speaking, if you telling people to "Just read the defence department's website".
Morally, China is trying to remove Taiwan's defacto independence, for reasons that completely ignore any idea of self-determination, whereas the US is supplying Taiwan with the weapons to choose.
There's nothing stopping Taiwan's democratic government and its people from choosing to give China control, since there are pro PRC parties in Taiwan, and even so--they have decided to resist PRC control.
You can, of course, argue the US should not give Taiwan the right of self-determination, that it should stay out of the affairs of other countries, since there are obviously economic reasons in addition to moral; but nonetheless issues of self-determination are at the heart--since the people and their well-being are always at the heart.
[1] https://en.wikipedia.org/wiki/Six_Assurances