I'm saying that if a country's currency stops being accepted as the main means of exchange within its borders then its government will use laws to restore that.

And if laws are not obeyed that's a police matter.

Concretely if stores stop taking fiat, and only cryptocurrency, to the point where it affects the economy, then you should expect laws preventing that. If that doesn't help then you should expect to see arrests happening.

Governments have the legal and physical ability to enforce monetary policy. Bitcoin nuts who say that "fiat currency is backed by nothing" are delusional. Several currencies are ultimately backed by nuclear weapons.

So in other words cryptocurrencies are only allowed to the extent that they don't overthrow the whole system. And overthrowing the whole system was the whole point, right? (well, that and buy heroin and make ransomware)