They want it to remain classified as Schedule I along with LSD and heroin, drugs deemed to have no medical merit while being highly dangerous. And they want everyone to believe that making marijuana available for medical purposes will lead to more crime.
The DEA and private prison groups depend largely on busting and imprisoning non-violent pot smokers that comprise at least half of all drug possession cases nationally. They rely on the 1930′s Reefer Madness film's propaganda and the "gateway drug" principle, which is the con by which most Americans are sold the marijuana threat lies.
It has been the rediscovery and further development of marijuana or cannabis's medical applications and recreational safety that have contributed the most toward the movement for decriminalizing marijuana possession. Even Washington, D.C. has readjusted it's marijuana possession law, which prior to this had the highest conviction rate for non-violent users than any other city in the nation.