I think things like bisq would be pretty easy to shut down of the government wants to, because fiat transfer is always government controlled.

Step 1: make a law declaring it illegal. Step 2: have undercover cop attempt an exchange, then arrest/fine the other party. Step 3: repeat until no one wants to exchange anymore.

Sure, it wouldn’t be fully effective - the illegal drugs are still around, after all - but it will be annoying enough that all legitimate uses will disappear.