I don't think it is technically possible to ban bitcoin, only centralized exchanges.

If a country decides to ban exchanges, it could end up creating an untraceable black market since people might start exchanging crypto <-> cash in the streets.

Intelligence agencies would probably not be happy to lose such traceability capability.

Drug dealers would be taking over this black market as it creates new incomes while simultaneously helping some of their money laundering needs.

Blockchain startup ecosystem and crypto friendly entrepreneurs would leave your country. You would lose all related tax revenues and high-paying jobs.