I mean, the US move was tit-for-tat for a decade of militarizing the South China Sea, threatening war against Taiwan, undermining the US economy through stealing trade secrets and sponsoring national champions.
> the US, after all, is allowed to militarize the South China sea
The U.S. doesn’t claim the sea as its sovereign waters. China does. (Which had the totally unpredictable effect of majorly pissing off every one of its maritime neighbours.)
Not true, China's claims are best known in the West because everybody hates/fears them. But there are others - like the dispute between Indonesia, Malaysia, and the Philippines regarding maritime borders.
> the dispute between Indonesia, Malaysia, and the Philippines regarding maritime borders
There are disputes over territorial waters and EEZs. China uniquely claims the whole damn thing, not as its exclusive economic zone, but its sovereign territory. The Philippines aren't asking for the right to tax ships passing through its EEZ, it just wants to fish and drill and mine them.
The article you've linked to explains that Taiwan makes nearly the same claims as the PRC in the South China Sea.
In fact, the famous "dashed-line" claims in the South China Sea were originally made by the Republic of China, before it was defeated by the Communists. This is a map from 1947, showing the ROC's eleven-dash line: [0].
The only difference that I know of between the claims of the ROC and the PRC is that the PRC has slightly reduced its claims as a result of an agreement with Vietnam over the naval boundary in the Gulf of Tonkin.
> Taiwan makes nearly the same claims as the PRC in the South China Sea
Taiwan doesn’t assert the claim [1]. There is sensitivity around explicitly abandoning it, as “changing the ROC’s historical claims would indicate—especially to Beijing—that the island democracy was abandoning its historical political identity and moving towards an inherently Taiwanese national identity, or even independence” [2]. To the degree Taipei has legitimately aligned with Beijing, it has been in the limited sense of arguing Taiwan is legally a real island, not an islet which cannot make any maritime claims [3][4].
Taiwan not only asserts the claim, but actually occupies much more valuable islands than the PRC does. Like the PRC, Taiwan rejected the Philippines' claims and refused to recognize the arbitration body's decision or legitimacy.
Tsai Ing-Wen doesn't want to look like she's aligning herself with China on this issue, but this is long-standing ROC policy, going back to before the PRC was even founded. It's not something the PRC invented.
To be fair many (all?) of china's southeast asian neighbors are hosts to US military bases. They aren't going to bite the hand that pays for their anti aircraft defenses.
I feel that if Chinese carrier groups were based out of Cuba, or were routinely conducting exercises right outside Chesapeake bay, the complaints would probably be reversed by ~180 degrees.