Imposing tax on cryptocurrency by government is not good enough to me. If you have your cryptocurrency as cryptocurrency without converting it to fiat currency in other to do local business, then I think you should be excused from paying tax.
Taxes for cryptocurrency can change public perceptions, which have so far been negative where they are not taxable, money laundering, etc. Then the public will judge cryptocurrency to support government programs, because without tax revenue, development will not be possible. After agreement with the government, cryptocurrency can slowly become a popular digital currency in the long run.