sure, and 1 UST = 1 UST, but it turns out that people who thought they didn't need to trust the asset held its value are considerably poorer than they were before.
Well, not really. Tainted coins is a real, growing problem that BTC hasn't solved yet.
In short, BTC is not fungible.
You have to trust that the restaurant where you're having lunch will accept BTC as payment. In reality, using Bitcoin requires the same trust-based infrastructure as everything else because the only way to buy anything with it is to trade it for fiat.