He proposed that psychedelic substances, used at proper dosages in an appropriate setting could, under the guidance of psychologists, alter behavior in beneficial ways not easily attainable through regular therapy.
Subsequently, he had developed a following for his turn on, tune in, drop out philosophy which was commonly understood to suggest that taking psychedelic drugs (in particular LSD) was valuable to average people.
Having been the head of only 7 doctors controlling the 7,000 patients in Manteno State Hospital, he had direct experience diagnosing a large number of unusual neurological conditions along with their treatments, useful drugs, and their effectiveness.
From the middle of an experiment on a frog's optic nerve, in his shirt sleeves, he was offered a tie to wear and went to Kresge for the debate with no preparation.
With humor and without losing the audience, Lettvin followed with an appeal on behalf of the "higher" mental functions using textbook and clinical observations as support material.
Lettvin asserted that psilocybin causes cognitive impairment that persists long after the acute effects of the drug have passed, based on anecdotal evidence.