> a public alternative with private transactions

This is exactly why governments should step in and regulate Visa and MasterCard, to prevent them from banning porn or other adult services.

If this kind of banning goes too far, there will come a point when even Joe Blow and his dog start using cryptocurrency. And once (truly private and anonymous) cryptocurrency becomes widely circulated, people will no longer need to exchange it back into fiat currency. Joe might start paying other people directly with crypto and eventually, perhaps even his rent, utilities, groceries...?

And then what? How will governments collect tax revenue?