Some countries that are not ready for cryptocurrencies will ban bitcoin, others will try to control the movement of coins by imposing their own regulations. Japan and other countries welcome and legalized bitcoin instead of banning it. In my own country, bitcoin is not yet legal but the government did not banned it and they've been studying the cryptocurrency for possible legalization in the future. If government ban the use of bitcoin, people might instead try to buy or sell coins in the underground exchanges.
It is happening now in some countries, some government has no vision in the crypto currency , they are scared to adopt the new kind of money which is good actually for the countries economy I think, they reject the possibilities in the future, They are regulating and stopping Bitcoin on spreading in order to protect their business and other stuffs.