Because the currency changes over time—we started with tea, and alcohol was the currency during prohibition, and gambling, but gambling is now legal even here in Halifax.... Cigarettes are legal, but still a currency for organized crime. So why do you believe that prohibition is part of the problem? It appears to me that once you cease to prohibit a currency, they either find a new currency, such as white-collar crime or identity theft, or use the taxation margin to continue to deal with the contraband substance.
On October 23rd, 2009. See this statement in context.