They can’t track who holds some crypto so they can’t get taxed from it.
But since ultimately we're going to exchange the bitcoin into fiat in order to buy something, we're going to be taxed. Whenever you cash out from the exchange, there's already a tax that you're paying. When you're receiving money from the remittance center, there's another fee (which is also taxed). And when you're buying something, there's also the VAT which is another tax. They shouldn't worry about tax as long as we can't buy things directly with bitcoins.
And also maybe they think that some people from their country think that it was use for illegal transactions like buying things that can be used against them.
Bitcoin can surely be used for illegal transaction. But so is fiat money, and far before bitcoin was invented, people are already using fiat money for illegal activities. They probably are still using it these days. Those that are in the syndicate will probably not use crypto as they transact quite large amount of money and the market of crypto moves a lot, even with PotCoin, a coin that was made for the purpose of buying and selling legal weed.
I think most of them wish but just afraid to legalized it since crypto currency is risk investment and they are trying to safe guard their citizens from loosing on it.
But at the same time they are limiting their citizens. There's still the possibility of making tons of money from it. I'd say people should have the freewill to do whatever with their money. It's just an investment, at the end of the day, which may or may not go right.
they want to protect their citizen , since much online business opportunity appear such as HYIP or other ponzi scheme there are alot people loss their money.and maybe government worry about cryptocurrency could be like that.
Then that particular government should hire a better information gatherer as they are clearly misinformed about this whole thing.