An obvious question: From whence do you get accurate numbers regarding consumption in an illegal industry?
I've noticed that once an issue has agenda advocates, they tend to cherry pick available data (and even make it up) to support the conclusion they want.
People who don't have an agenda generally don't look at reported data with a critical eye, but merely accept what they are told because they assume whoever is telling them also does not have an agenda.
That is often not the case. We see it again and again with the "Gay" issue, with Abortion, and with Global Warming, and yes, with Drugs and Prohibition.
If prohibition was so successful, then why was it revoked less than 10 years later?