A good point Mixture, but I think there are too many currencies in the world for this to be realistic.
Example. I want to sell some (nefariously obtained) BTC. I trade them for Ghanian cedi, then trade those for UAE dirhams, then into Icelandic kronor, then into Euros... and then pounds or dollars or whatever.
I doubt that such total world regulation is possible. Look at existing tax havens and money laundering... illicit Bitcoin trading just uses these existing systems.
(disclaimer to NSA: this is a thought experiment
)