I'm gonna drag out something I wrote up in another thread, some while back, actually, my first gilded comment:

It's time to reform drug policy in the United States from the ground up.

Trust me. I agree wholeheartedly, but the issue is so convoluted, at this point, that it would be immensely difficult to completely rebuild the entire set of laws that make up Drug Policy in the United States.

Consider the beginnings of the current War on Drugs, which started near the end of Alcohol Prohibition. During the Prohibition, a fairly large Federal Agency had been built to help enforce the Eighteenth Amendment. When Prohibition failed and the Eighteenth was repealed, there was serious debate on what to do with this bureaucracy. Enter the debate on various recreational drugs and pharmaceuticals; marijuana, opium and its derivatives, ether, and so forth. The whole mess primarily started by Acts and Bureaus created during and immediately after the Prohibition, including the Federal Bureau of Narcotics, a precursor to the DEA, and spurred forward by Harry J. Anslinger, the FBN's first commissioner. He was the man responsible for making marijuana into "The Devil's Herb" through the massive use of propaganda, supported by William Randolph Hearst, who owned large stock in lumber to support his newspaper businesses, and saw hemp as a direct threat to that business. Needless to say, during that time period, it was easy to attribute cannabis as some evil date-rape drug, used by minorities, and likely to propel any user into a raving, murderous rampage.

Fast-forward through history, including the counter-culture movement of the 60's and 70's, which associated marijuana, LSD, and other psychedelics with the "lazy hippies", followed by the 80's and the cocaine and crack push, spear-headed by Reagan, and reaching it's zenith with the 90's DARE and "Just Say No" campaigns, the fact remains that, for the better part of 3 generations, many Americans have been quite complacently brainwashed to believe that anything other than tobacco and alcohol will become a one-way ticket to addiction, death or prison. While, yes, opinions on marijuana are improving across the board, but there is still a stigma that associates it with lazy burn-outs who accomplish little.

TL;DR - The issue isn't the policy itself, but the culture that has been built around it for decades, first with institutionalized racism, then with economic and social pressure. ("You won't get a good job/degree if you sit around smoking pot, all day.")