I think that the reason for governments in this area bans cryptocurrencies is the rampant criminality there.
Governments probably try to regulate criminals and try to close every funnel of funding their illegal activities. They are not opposed to the technological innovation of bitcoin but maybe right now they don't have any other reason to allow it.
If this is indeed the reason it would be unjust. Cash, is as easy for criminals if not easier to use than Bitcoin. At least with Bitcoin you have recorded transactions on a public Blockchain, where as cash goes under the radar, and isn't public knowledge. Plus, cash is already used on the mass for criminals exchanging services, and goods.