I can't blame him for being apprehensive - he would probably have a heap of crap to work through
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. I know I did initially.
I am sure with his connections he will probably find some experienced guidance, both to give him the support he wants available during it and to explain to him why it's not clinical support he needs.
The crucial thing will be to get him to the point of having a positive high dose experience. If he comes out of it saying that these substances just make you see a few colours (e.g. Schultes) or that they make you temporarily insane, that won't be helpful to anyone. It need not be a religious ecstasy. Just something to remind him of the incredible landscapes of consciousness should get the cogs turning.
What really surprises me is that Dawkins hasn't tried them already, given that he has obviously done a good deal of reading on the matter. When I read the Doors of Perception as a teenager, seeking out that experience for myself became an obsession that lasted for years until the curiosity was satisfied. It sounds like he has the same burning curiosity about the nature of our existence as I do, and yet he has not sought it out.... ? This brings me back to my opening sentence.