Governments are struggling to regulate cryptocurrencies, so I don’t know how they would begin to tax them. I think the best they could probably do is tax exchange of real-world goods, such as real estate, which is much harder to keep anonymous. So we’ll probably see an increase in taxation for things like land, real estate, and other physical goods that are exchanged using whatever form of currency.

As for criminals, for sure, but I’m not sure cryptocurrencies increase the amount of criminal behavior, and a lot of behavior in the regular financial
system comes pretty close to criminal (e.g. subprime loans), so I’ll bet we’ll come out ahead in the end.