Lot of countries do not allow to use crypto currencies and they discourage using them. However as far as I feel, trading with crypto is not that harmful for the economy of the country. As an example, if a person has Eth and someone from another country needs to buy Eth, that buyer needs to pay the seller in terms of dollars. Then that seller needs to convert that Dollars to his native currency which means it creates a the demand for the native currency and increase the value of the currency. May be the government is unable to add a tax on such transactions but it is beneficial for the currency used in seller's country.
What do you think about that?
There are many reasons for a country not to use crypto currencies. But the main reason is still the law of their country has no law for crypto currencies if the dispute occurs, the effect may be on the national currency. The market for crypto currencies is small and risky.