Here's a theory of mine. I don't have any evidence to back it up as of yet. I'm not trying to sound like a conspiracy theorist, but here's what I think.
The whole war on drugs was never a war to begin with. It seemed like a continuous triangle for three industries to get paid.
1. Drug dealers make tons of money in an illegal business sector, the government allows them to do this as long as they don't get too sloppy and make it too obvious. This illegal business sector has a real demand, but its illegal. The government, however, still wants the money that sector makes. Then when that dealers hits a certain level, federal agents swoop in, shut the party down and confiscate all the money and dope. The money and dope, of course, goes back to the government.
2. After the confiscation, the drug Kingpin and all of his workers are sent to prison. So now the prisons are making money off of the inmates' labor.
3. The government then turns around and puts the dope right back on the street and repeat the process again. Of course they have to bust the petty dealers to make the war appear real. I'm not making a conspiracy out of it. To me, it sounds like pure economics.
I really don't understand why the government would even go through all this when legalizing certain drugs would make them more money than doing it on the DL.