It is enforceable at the citizen and institutional level. I know many decentralized cryptocurrency advocates tout the fact that no government can literally modi

It is enforceable at the citizen and institutional level. I know many decentralized cryptocurrency advocates tout the fact that no government can literally modify the blockchain. While accurate, that is not the point. Governments don't need to do that because they basically have free reign to enforce laws and regulations on its citizenry. Sure you can set up a miner in China, but if the authorities find out you're going to prison. The State might not be able to stop all mining, but they will definitely force it underground and make it a very risky thing to do. A total prevention of an activity is never the actual goal of a ban, the real goal is just to stop the vast majority of it from happening.