For those who never experienced the Grateful Dead concert scene, whatever town the band would play in would become the biggest open-air drug market in the country. Wide-open sales of most drugs, especially LSD, happened in the parking lots. Just as the CIA flooded black neighborhoods with crack, they were likely behind much of the LSD that was available at the shows.
It is true that most people at the shows were good souls. However, LSD was used to destroy the anti-war movement in the 1960's, and the large-scale distribution through the 80's into the 90's was not being done with good intentions. Of course, people at the shows would have never believed that the Central Intelligence Agency was involved. At this point, it appears undeniable.
Months ago, someone said that they had a friend who was going to record some music. As best as I can remember, they said something like the studio wanted to include some sort of low-hum into the tracks that wasn't even audible in the final mix. It sounded like it almost had to be for nefarious reasons.