you are talking about taxes after exchanging cryptocurrency for a fiat currency, cryptocurrencies doesn't have taxes (well transactions cost kinda work like a community tax but in the real world there are also transactions costs and taxes), exchanging from crytpocurrency to fiat has.

What stops you from exchanging your crytpocurrency to a fiat currency that doesn't impose taxes?

Good point and I agree. That said I still don't think this would count like a true libertarian experiment because -like you point out- it is in the real world where you still have to abide by the rules of government/society.

But yeah, this is probably the closest we have gotten to a libertarian test-drive through technology.