YES

Countries can ban the user of cryptocurrency completely depending on their own discretion. One major reason is it threatens their authority of everything. Cryptocurrencies are made to be decentralized, giving the power back to the people and that's what they are completely afraid of.

With a definite reasoning and authority, they can completely ban cryptocurrency especially if they introduce a new form of technology that benefits more equally. 

Another reason of banning it for me is crytpocurrency brings chaos and war to countries. Because it is decentralized and some transactions are encrypted, they are known to be used for fraudulent activities. Criminals, drugs, and hidden transactions were done using cryptocurrencies because they cannot easily be tracked using it.