That's gotta be one of the best stories I've ever heard cobbled together from one, tiny, misquoted piece of information.
Almost everything this guy says is wrong, however very entertaining. The one piece of accurate information, and I found this very funny because I instantly thought of it when I read the title of your post, is that there was an archeologist, about 20 years ago I think, that did find fossilized remains of psychoactive mushrooms around the cook fires sites of either H.S.Neanderthals, or H.S. Sapiens.

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It is funny. I have to admit, at its core, I think there's something interesting in the concept itself. It's the kind of thing, however, that just seems to attract folks who are going to dive right overboard and leap to extreme, nutty conclusions. Connecting up mushrooms with a universal consciousness manifesting through spores from space is just whacky. I can see how someone might express that view, because the psychedelic experience does go that direction almost inevitably. I suppose the problem is that people should form their theories AFTER they experiment with these things not WHILE they are experimenting....

It seems logical that one of the early motivations in human development and civilization was the cultivation of certain plants that were have more religious than nutritional value. After all, cultivation on a large scale (for nutrition) would seem something of a leap in technical process. Were one to premise the cultivation of small, highly valued "crops" as a step then the progression seems more incremental.

Also, brain development in appreciation of the effects of those "drugs" seems to make a certain sense as well, particularly if it goes with the early stages of cultivation as that constant would be more likely to have a constant and, therefore, "environmental" impact than would accidental consumption.

The main problem, of course, is that it isn't actually science. There's not a lot of experimental or even observational verification of the theory. I suppose one could do some really extensive studies on the effects of such things on primates, but we're talking about evolutionary time, so it's hard to do experiments to support the idea.

The other problem is that it seems impossible to depoliticize something like this. Proponents are going to get their views from their opinions on drug use. Opponents will as well. I don't see a lot of people getting past their mindset to look at this one realistically.