Failed CIA mind control experiment triggers the war on drugs
Back during the golden age of LSD experimentation from the 1950s - 1965, basically anyone could get their hands on LSD. Though also researchers were trying to figure out what LSD is good for.
One of the early findings hinted towards mind alterations which the CIA quickly hopped onto it for personal gain. Though sadly the object they were testing on, got loose and told all the college kids of his experience.
Now that would all be fine if there wasn't a war going on in Vietnam and they were looking for troops. But the hippies and/or drug users were declining to serve for the country, which was unheard of at that point of time.
So one could conclude that mind opening drugs that break the confines of the matrix, break at the same time the traditions of the government, and thus to prevent this from happening we got to ban the initial spark. Since an open minded person cannot take orders, thus has little value to the government.
The ban is called the war on drugs.
Source: Netflix - How to change your mind - Chapter 1: LSD