The biggest problem with your thesis: In a nation governed by 60,000+ pages of federal law - everything is illegal. Federal prosecutors have been known to joke that they can indict the typical American for three felonies a day (those hilarious feds).
People have been using drugs since people have existed. Criminalizing behavior that's been going on for eons is a fool's errand.
No thinking person who claims to love reason and liberty can support prohibition. Just ask Milton Friedman, who said it better than anyone else ever could - http://www.theagitator.com/2012/11/09/milton-friedman-the-war-on-drugs-and-last-tuesday-night/