I think some of McKenna's ideas are absolutely brilliant. And I think some of his ideas are completely stupid and ridiculous. He's the only guy I have this opinion about! (most of the time everything a smart person says is more or less smart, and everything a stupid person says is more or less stupid)
I'll start with the one I think is stupid, TimeWave Zero and the acceleration of time and the end of the world at 2012 and all this stuff. Basically everything he was working on the last 5 years of his life. All this stuff is totally irrational and not based on evidence, a real departure from his previous genius that I find regrettable because it stops people from finding out about his really interesting ideas. It's still hard for me to believe a man whose intelligence I admire championed a doomsday hypothesis... how embarrassing. And sadly this idea has enjoyed some success in the psychedelic community. Other people have written books connecting psychedelics to a 2012 apocalypse, such as Daniel Pinchbeck. In an area of life so important for human health, and so crippled by lies and superstitions, another piece of irrationality was really the last thing we needed.
Now for what I like about him. First his ability to cogently describe the experience and give "Trip Reports" is very, very impressive, especially to someone who reads a lot of trip reports on Erowid and sees how incoherent most of them are. Absolutely classic is his description of his first DMT experience. And all of his descriptions of his interactions with "The Mushroom" as he calls it are edifying.
The best thing he did, in my view, is the theory about the origin of human consciousness that he puts forth in his book Food of the Gods. The idea that mushrooms, with their remarkable tendency to increase neuronal connectivity and engender creative expression, were responsible for the sudden explosion in the size of hominid brains (the single biggest mystery in evolutionary biology), is an idea that has occurred to many people, but the way McKenna put it down and supported it with archaeological evidence was a tremendous contribution. I don't know any mainstream biologist who has put forth an explanation even remotely plausible for the sudden swelling of the human brain, which happened in just a few seconds in evolutionary time scales, McKenna's is the only one that is consistent with the evidence. And of course his theory is completely ignored by mainstream evolutionary biology. Which is really astonishing when you think about it - just because the government made a certain plant illegal, scientists with less courage than McKenna simply refuse to even consider it in their theories! I defy any biologist to look at his evidence and not be convinced.
I've also gotten a ton of interesting other ideas from him about drugs and society. The idea that culture essentially brainwashes you and controls you and psychedelics are the way to free yourself from cultural programming. The idea of foods and drugs not being separate categories, but just different phases along the same spectrum, different types of the same thing, substances that interact with the body. And lots of other interesting ideas! McKenna is my favorite psychedelic writer, I like how his approach is scientific yet openminded. But my favorite thing about him is just the clarity with which he describes the completely strange and unusual experiences he's had with psychedelics.
