We've been running this shadow economy for the last 5 years now. I'd say if you want to stop it, start with all the ponzi schemes. Take those down, we don't really need those. Governments can stop fiat to bitcoin exchanges, but they cannot take bitcoins away from people who own them. And you cannot really take down this "shadow" economy system that we have been operating. It's just impossible. Just good luck turning off the internet.
There is no reason to ban bitcoin at all. It is just a token or a kind of goods, or credit points. All those things are legal in many countries. Those things can also exchange for cash or various currencies. the only difference between bitcoin and other goods is that bitcoin has finite supply unlike most currencies, thus the value will not drop all the time.