It turns our passive, private, spontaneous appreciation of popular culture into something active, public and market-driven. It leads us to confuse self-expression (which is, of course, all about us) with art (which more generously “speaks to us even though it doesn’t know we’re there”). It has created what Mr. Siegel calls the first true mass culture, though he cites critics who in 1957 worried about how culture could be degraded by the masses. Culture for the masses, he says, was a worry of the past. Culture by the masses is what is being born in the present and will shape the future.

Peppering his argument with potshots at writers (among them Mark Dery and Malcolm Gladwell) who view any of these developments enthusiastically, Mr. Siegel both defines and decries an array of current misconceptions. We are being persuaded that information and knowledge are interchangeable, he claims, when they are not; we would have citizen heart surgeons if information were all that mattered. And mainstream news outlets, which Mr. Siegel is otherwise delighted to assail (his love-hate relationship with The New York Times is particularly intense), suddenly look worthwhile to him by virtue of their real, earned authority. Better the old press than the new tyranny of bloggers. Their self-interest, he says, makes them more mainstream than any standard news source could possibly be.

The vindictiveness and disproportionate influence of the blogosphere is a particularly sore subject. Who is it that “rewrote history, made anonymous accusations, hired and elevated hacks and phonies, ruined reputations at will, and airbrushed suddenly unwanted associates out of documents and photographs”? Mr. Siegel’s immediate answer is Stalin. But he alleges that the new power players of the blogosphere have appropriated similar powers.