The USA is also willing to defend Taiwan and currently the US has carrier groups in the south China sea. This suggests that the idea of building chips in the US may be a diplomatic courtesy and arguably an incentive.
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Personally, I think we're at the point where the US would consider the costs of Taiwan's defense well beyond any potential benefits. It's too economically integrated with China, and the sheer number of bodies it would take aren't worth the moral victory.
Hong Kong is the writing on the wall. China wishes to restore integrity to what it regards as its territory.
TSMC must open facilities in the west because its Taiwan facilities are too dangerous to leave in enemy hands. It has to invest in capital outside of any potential conflict zone if it plans to exists over the long-term as a profit-making entity.
It's not merely a moral victory. And while I myself would pick up a rifle for 24 million people, it's not even that.
You can't simply let your allies be invaded. It's lethal to all of your other alliances. America failing to defend Taiwan is the end of the Pax Americana, and America knows it.