Why?

With this plant glaucoma sufferers would be able to grow their medicine in their back yards for minimal cost. Because of the law that congress passed in 1937 pharmaceuticals are able to charge hundreds of dollars for minute amounts of synthesized THC marketed as Marinol. That fact speaks volumes.
That fact explains why Democrats and Republicans will continue to continue to wage the "war on drugs." The pharmaceutical industry buys more congressmen from both parties than Jack Abramoff. That's one more reason why we need another political party to challenge the complacency of the current duopoly.
The so called war on drugs also continues because our intelligence agencies need a black market in which to raise funds for their black ops. Does anybody remember Ollie North rhapsodizing about the "stand alone, self financing off the shelf organization"?
This culture glamorizes the use of drugs for everything from erections to regimented sleep patterns. The FDA continues to give quick approval to the latest pharmaceutical wonders while the peddlers misinform the authorities about the efficacy and safety of their products. Lawsuits are making their way slowly through the courts as a result of the deaths that resulted from the shady approval of Vioxx.
Some over the counter pain reliever whose name I've managed to block from my mind is running some commercials in which the characters say that for every new pain they needed a new medication. And you want me to believe that we're fighting a war on drugs?
We sorely need to define our terms. What drugs are we waging war on? What are the criteria that we use to decide which drugs get the FDA blessing? It seems that the primary requirement is that the drug be manufactured by a large, for profit corporation; nature's way is verboten.
This particular war of which I speak is actually a war on our freedom to pick the intoxicant/medication of our choice. Gussie Busch and the rest of the alcoholic beverage industry spend lots of good money to make sure that theirs will continue to be the only legal intoxicant.
The common thread through all these reasons why the hemp plant is illegal is greed. Not only does the black market create a need for more jobs in law enforcement and corrections, the opportunities for corruption are endless. Even members of the military at Fort Huachuca and Davis Monthan AFB have been busted smuggling illegal drugs. Countless Border Patrol agents have also given in to the temptation of easy money. Al Capone and the latter day, cocaine dealing Scarface made their millions because of prohibitions which define vices as crimes - thus making them irrationally profitable. But that's precisely why the Republicrats will keep the black market in business.