It's been shown that the government profits from making drugs illegal; much more than they would from taxing it. When you make a drug illegal, you create artificial scarcity and jack up the price. This illegitimate money now has to be laundered and paid for by income tax. That doesn't even count all the crazy fucked up backdoor deals that rogue law enforcement has with the mob. They can also siphon tax-payer money away from the War on Drugs without anyone knowing about it, in certain situations. Oh, did I mention that prisons can be run for-profit? Let's fill up our jails with people that don't deserve to be there and siphon more taxes there! Hurrah!