The only convincing explanation of the benefits of stablecoins I have seen is that it is a backdoor for implementing narrow banking, which libertarians love and economists and central bankers hate (as it would cut off credit to the economy).

A narrow bank is a bank that takes deposits but doesn't make loans, basically parks the cash at the central bank or into risk free instruments. So it provides you with payment facilities, very low interest rates, without the credit risk that comes with a large bank that has exposures to all sorts of risky businesses.

Everything else is either temporary benefits of arbitraging slow moving regulations (but KYC, consumer rights, money laundring regulations, etc are quickly catching up), or as you suggest, some non sense about a zero trust system (crypto / public ledger) that fundamentally relies on trusting a custodian (so you might as well use an oracle database and spend in licensing what you save in energy cost!).