It's not often one has a ringside seat for the second coming of the messiah. It was a thrilling event, well worth the entry price. Oh, yes, and I'm worried about the mental health of a Scottish columnist and broadcaster who seems to have become unhinged in these apocalyptic times.

Let me explain. The Edinburgh International Book Festival has been exhibiting its usual vibrancy, spilling controversy about matters such as Princess Diana's foibles and Ian Rankin's views on women crime writers. My favourite turns have been Richard Ford, Marista Leishman, growling McIlvanney back at his best, Nicola Barry, Terry Eagleton, Marina Warner and John Gray.

And, of course, the return of the big guy. The joint was jumping as he walked in, once again turning the RBS main theatre into a revivalist tent. When Richard Dawkins made his entrance, we were privileged to witness a miracle: Muriel Gray's normally sharp and lively brain mysteriously turned to mush. Yes, in the presence of the sun god, the spiky columnist's critical faculties went into instantaneous meltdown. She became cheerleader rather than chairperson, groupie rather than griller, in a toe-curling display of sycophancy. Oh dear.

Not a single searching question was asked from the chair as its apparently besotted occupant pronounced religious believers "thick", before going on to assert solemnly that Dawkins's book, The God Delusion, had closed the debate about God. She genuinely seemed to believe that since the scientific Bhagwan had spoken, awed silence was the only appropriate response. Nurse! Such was the cultish mood it would have been no surprise if Sister Gray had invited the congregation to rise and sing "How Great Thou Art" to the smiling demigod seated on the platform.

Now, I happen to think that The God Delusion is a vigorous and helpful contribution to the debate about God, and said so in a review in this newspaper. I've been reading quite a few tomes by the so-called "new atheists", and enjoying them. Daniel Dennett's Breaking the Spell raises intriguing questions, and Christopher Hitchens's God is Not Great is a wonderfully polemical read. I've always been a fan of Hitchens, and his outrageously extreme book is the most entertaining and best written of the bunch.

The God Delusion has been riding high in the best-seller lists in America and Britain, and deservedly so. Everyone interested in religion should read it. It is much better than the author's tawdry television documentary entitled The Root of All Evil, in which the great man spoke to a ghastly collection of the most deranged religious bampots in the world but managed to avoid conversing with more than a single Christian or Muslim with at least one brain cell. Mind you, if people like Rowan Williams are all "thick", why bother?

Here we get to the core of the Dawkins delusion. I would have thought that if an academic were going to make a critique of any position, he or she would be obliged to take on that position's most able exponents. You don't need to get far into The God Delusion to realise that Richard is actually theologically illiterate. If he has read any modern theology, he wears his learning so lightly no traces can be detected by the naked eye. In his own field of evolutionary biology he would rightly object if an academic opponent made a vulgar caricature of his discipline, yet where religion is concerned, he is almost proud of his contemptuous ignorance. This is perverse.

When I encounter some of Dawkins's more extreme writings, I catch a whiff of other literature I have read. Yes, extreme evangelical Christianity. Have a look at his website (www.richarddawkins.net) and you'll see that it's a mirror image of some rather zealous and dogmatic religious sites. Richard Dawkins is an obsessed evangelistic atheist autodidact, a dogmatist whose extremism is even starting to irritate some of his fellow unbelievers - such as philosopher Thomas Nagel, who described The God Delusion as "a very uneven collection of scriptural ridicule, amateur philosophy, historical and contemporary horror stories, anthropological speculations and cosmological scientific argument".

Dawkins and Dennett and Hitchens raise good, sharp questions which will hopefully produce a religious winnowing, a needed chastening. But when the new atheists puff out their hubristic chests - calling themselves "brights" - and claim to have got things sorted, they become as unattractive as any triumphalist Christian cult leader. Everything in the Gray universe may be black-and-white, but in the real world, religious people are falling down manholes and atheists are falling down godholes. This is much more fun, as well as more truthful. It was good to have Dawkins back in the big tent, but it's time his own blessed assumptions were seriously challenged in a debate which is a million miles away from closure.