There is a common pattern in history of "unholy enemies" - groups of people who are presented by leaders to be of such evil nature that the general populace should be willing to sacrifice their lives, freedom or well-being to fight them. These have been the Jews in Nazi Germany, and the Kafirs in Islam. In modern society, drug users now serve as an unholy enemy for which the government can undermine Liberalism and gradually repress the people.
Yet, drug users are no such enemy - they do not pose a threat to society. Plus, they are people in need of help, not in need of being hunted and prosecuted.
The legalisation of drugs will put a stop to the irrational trend to make drug users an unholy enemy and for the government to undermine the individual rights of the citizens. There is no good reason to undermine individual rights, much less one that is useless and pointless as trying to "win" the war on drugs.