Essentially the author is taking aim at the plausibility of humans using psychadelics throughout history and time on the veracity of the historic and fossil records.
Which is fine. Because most of the ideas are derived from interpretations of scant bits of evidence to begin with. The whole narrative is much closer to a group of friends theorizing what the first ape to consume psilocybin may have felt than scientists and historians enshrining a proven theory. But I think the author gets a little stuck by not really accepting most all of these theories are predicated as fanciful and speculative.
Stoner culture isn't the same as the medical marijuana resesrch. But the former is quite marketable in its own right. Same thing here.