Biggest benefit of using blockchain and cryptocurrency here is open trust (this term is the best way I can think about describing this). Any internal database is subject to all kind of human and technical errors. But with a network of trusted parties that solves the Byzantine Generals Problem. This becomes secure and trusted as trust is given. No one can hack it at will without taking the 50% of the network down and compromising multiple entities. This is a bizarre technical, social and economic feat. I wish Apple was the one pulling this instead of FB. But quite certainly there are more FB users than iPhone users.
Not true for stablecoins, which aren't really cryptocurrencies. The most important single-point-of-failure in currencies is the supply mechanism, which must be trusted. The supply of centralized stablecoins can't be trusted. It is open to human greed, errors and hacking. Do you trust Mr. Zuckerberg having control of the future money supply?
Centralized stablecoins should be illegal, because the issuer can print money from thin air without collateral, unlike banks which are regulated and the money supply is controlled with interest rates.
