The war on drugs, just like many other wars against freedom, exists to gradually take the freedom of people away. The war on drugs doesn't stop people from becoming addicts if they want to. Rather, the war on drugs gives authorities the right to dig into the private lives of people just to find out if they use drugs or not... a reduction in the freedom of privacy.
The drug war is all about taking freedom away. There are other ways to slow down drugs, such as advertising.
In free countries, the drug war actually increases the creation and flow of bad drugs. Odds are that if people were allowed to smoke pot or coke, and use mescalin freely, nobody would have had the need to develop things like ecstasy or meth and who knows how many other drugs. These drugs would never have been developed.
Further, the amounts of medical drugs in pills is almost microscopic. If these drugs were in broader use, the problems they would produce would dwarf illegal drug problems. This is exactly what is happening. People are finding out how to make medical drugs and sell them on the black market as psychedelics, but in much larger doses and quantities than you would ever find in medical drugs.
If there is going to be a drug war, it should be across the board, against the medical, as well.