Which I acknowledge above. You can ban exchange to fiat but it will only reduce value, not completely eliminate it as there are protocols which derive value from defi ecosystem itself.

I.e people will start directly using these currency for payments (which they already do) without exchanging to fiat. The stability is maintained by the defi collateral and shared acceptance.

So you would have to ban everyone to accept crypto currency and so on as payment but that is very catastrophic decision with large implications.

It also doesn't help crypto completely eliminates centralized authorities when moving across borders.