Tax is a legitimate source of government income if all of us have good income to pay taxes to government that is legitimate.
I agree with your opinion, that tax is a source of state income. Without taxes, the country will end. But tax on cryptocurrency? I don't think that is possible because cryptocurrency is a decentralized digital currency while the trading system is peer to peer. So it is difficult to monitor what crypto money is used for or where. How to anticipate it is not by imposing taxes on crypto, but the imposition of taxes on goods / services paid with crypto money.