the government has no right to tax that is not provided by their laws. Cryptocurrency has an indefinite status in the state. It is therefore not subject to tax
They have the rights since they are the one who is controlling the society of a country and they can just simply create a law that can shape out and regulate the usage of bitcoin and even put tax with it. And for sure, if the government will see that they have a chance to get some profit from taxing crypto currency, they will.
Well
it will be very hard to regulate and impliment this as well because we all know that what separates crypto from other currencies is it's anonymity and privacy. It may take a very long time before governments can manipulate crypto like fiat
This doesn't change a thing in the end. They can just make it taxable, and voila, you are obliged to pay the tax. If you don't and don't intend, then you are going for deliberate tax evasion, which may be a criminal offense in many countries. If you got caught red-handed, you will be penalized and most likely made into a criminal with all ensuing consequences...
And someone will surely end up exactly like that