You're asking this question, but your assumptions are all wrong.  Stablecoins aren't created to compete with the USD or any other fiat currency as far as I know, and their purpose isn't to destroy fiat at all.  They basically function as a substitute for fiat on crypto exchanges, so instead of cashing out your bitcoin for USD, you trade it for Tether or some similar stablecoin--so you're never really dealing with fiat currencies at all.  I'm not sure what the advantage is of this, because I've never read a good explanation anywhere.  Those are just my own thoughts.

Kind of makes me think of Libra and why Facebook wants to create a stablecoin.  My guess is that it would allow them to collect data on users' financial transactions, which they can't exactly do right now when people are doing transactions through their banks.  I don't know what people are supposed to use Libra for, but I'm assuming it would be for FB-related stuff.  I'd love to hear somebody's input on that if they know something.