PEOPLE WHO LEAVE cults and religions rarely do so quietly. More often, they feel an urgent need to tell the world that the cause which they so recently worshipped is a sham. In their disillusion they do not feel calm; they shout a lot.

Andrew Keen joined the first internet gold rush. But he did not get rich. And he began to wonder if all the claims that were made for the digital Utopia he had been selling really added up. Are crowds really wiser than trained professionals? What do social networking sites do about paedophiles? Why trust bloggers more than journalists?

These are excellent questions. But this sustained and pessimistic rant at the claims of progress made by the digital gurus doesn’t have many of the answers.

Keen doesn’t seem to realise that he has himself been infected by the virus of Silicon Valley hyperbole. For every exaggeration from Wikipedia, Google and Amazon he has an apocalypse to match. The amateur is hijacking the role of the professional; the geeks have demolished the “dictatorship of expertise” with disastrous results. If everyone can publish “user-generated content” this only means “user-generated corruption”. Deceit, junk and pornography fill the world’s screens.

Some deep breathing and sense of proportion and of history would help. If I collapse while reading The Cult of the Amateur, do I want bloggers in pyjamas diagnosing me? No, I want a trained doctor on the case. Technology changes are rarely reversible and almost always tilt the playing field for business. Digital music down-loads and the ability of record and replay TV programmes alter for ever the business models for recorded music and television. In such changes, there are winners and losers; nothing new there.

Keen has little faith that people can sift the vastly increased amounts of information and entertainment at their fingertips. He touchingly believes that there was once a simpler time when newspapers, television and radio relayed truth beyond dispute.

Much as journalists might want this to be true, there was no such golden era, ever.

Open societies argue with themselves. Digital communications multiply that argument and create a temporary Babel that might seem to drown out common sense. This book is sprinkled with complaints from intellectuals, including a splendidly pompous moan from the German philosopher, Jürgen Habermas, that they aren’t being listened to as much as they were. Yet Keen himself has had no problem getting publishers on both sides of the Atlantic to help him to argue at length that the emperors of the digital kingdom aren’t wearing any clothes.

An explosion of new voices doesn't mean an indefinite anarchy of ideas. The more information highways we build, the greater the demand for maps to help us to navigate them. That needs discrimination and judgment. Provided that people are trained to think, they can choose between good and bad – and argue about which is which. Keen only pauses for a single paragraph to broach the enormous issue of whether the internet and e-mail are actually changing the way our brains work. Now there’s a book to be written.

The Cult of the Amateur: How Today's Internet is Killing our Culture and Assaulting our Economy by Andrew Keen

Nicholas Brealey, £12.99; 240pp

Buy the book here for the offer price of £11.69 (free p&p)

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