They don't really need to tax you.

In my country, what they did was, they regulated every cryptocurrency here. So whenever you wanted to convert let say Bitcoin into fiat (money), it will surely have fixed fees depending on the amount of what you wanted to convert. Also, here you can Bitcoin into specific Banks and will automatically be converted into fiat, though there may be no fee but at least they regulates it.

Since it was implemented here pretty quickly, personally I think its still convenient, and I think the fees are not that very high, so I'm used to it.