I strongly agree on your opinion that, bitcoin is banned in some countries because they don't know how to demand taxes from this, and still fear for the economy of the country. And adding also my opinion that, the main reason for this ban is it's really really difficult to control Bitcoin. Bitcoin transaction is anonymous so it's nearly impossible to find out the owner of any transaction, beside countries banned Bitcoin because their technology still not developed enough to control Bitcoin and its disadvantages to prevent crime take advantage of Bitcoin. In addition, Bitcoin is decentralised and thus these governments cannot control it, the main issue with this is that they cannot tax it effectively.