Outright criminalization only drives the demand for the drug to the illicit market.

CNN: Banning fake pot won't make it go away

Illicit trade is age-old, a continuous facet and side effect of market economies or of commerce in general.

NPR: Tracking the World's Black Market: 'Illicit'

From a rate of 3.4 ringgit to one dollar, the currency was devalued to 3.8, well below the then market rate, so investors had little incentive to take their money out by illicit means.

ECONOMIST: The big clean-up

Illicit trade's ancestor, smuggling, traces back to ancient times, and many a "thieves' market" survives in the world's commercial hubs.

NPR: Tracking the World's Black Market: 'Illicit'

For now, the size of the bitcoin market is so small that it could be difficult or costly to move and exchange large amounts of illicit funds.

WSJ: Web Money Gets Laundering Rule