If Barack Obama is the most admired black man in America right now, it may be no exaggeration to say that John McWhorter is a candidate for the unpopularity prize. Which is an odd thing to say about a courteous academic from the arcane realm of linguistics. Yet by venturing onto the mean streets of hiphop with a dispassionate critique of a multimillion-dollar industry, he risks becoming a target of drive-by shootings by enraged academics, book reviewers and bloggers.

McWhorter is not all that surprised that critics have given him a pummelling. He lets out a sigh of resignation: “By its very nature, this book cannot be received fairly. It’s difficult for people to separate feelings from thought. Tempers are going to have to cool.”

So, what is the incendiary message of his book? Interestingly enough, McWhorter doesn’t align himself with that beleaguered minority of sceptics who see rap as a cultural dead end, a bloated, bragging perversion of the American Dream. He may be in his forties, he may be a devotee of musical theatre (Cole Porter is one of his deities, and he met his wife at a sing-along cabaret bar), yet McWhorter admires the best that rap has to offer. He likes the Roots; he occasionally listens to Snoop Dogg while cooking dinner.

All of which makes him sound like your average right-on professor. McWhorter’s animus is reserved for those pundits and intellectuals who see in hiphop the makings of a social revolution, guided by rappers whose outspoken commentaries on race, poverty and violence have made them, in the famous words of Public Enemy’s Chuck D, “Black America’s CNN”.

Nothing could be further from the truth, McWhorter argues. Far from being truth-tellers, he says, so-called “conscious” rappers recycle endless clichés and conspiracy theories about inner-city blight, the drugs trade and Aids. Instead of generating a desire to change the system, rappers and their acolytes in the media and academia simply encourage a sense of passivity. “Insisting that things are still so simple that black people need to get together and rise in fury against an evil oppressor makes for entertaining hiphop,” he writes. “It sounds good uttered fiercely and set to a driving beat. But this way of parsing things does not correspond to what black America really needs today, as opposed to what it needed 50 years ago.”

Naturally, hiphop’s defenders have been quick to respond. In the harshest riposte to appear so far, the LA Times’s reviewer dismissed McWhorter as “smug and beleaguered”, insisting that he had got the politics all wrong: “The idea that hiphop in 2008 is ‘antiestablishment’ and ‘by definition about protest’ is equally perplexing, given that so much of hiphop has embraced the trappings of materialism in recent years. McWhorter glosses over a complex reality in which rappers are record-label CEOs and corporate pitch men, small-business owners and schoolteachers.”

The author is unrepentant. One of the most common responses to the book, he says, is that his thesis misses the point because hiphop is now more about bling than social protest. He disagrees, arguing that big-selling stars such as Kanye West routinely recycle political slogans. In any case, McWhorter’s argument is more with the intellectuals who praise hiphop than with the performers who make the records.

“One reason I wrote this book is that I worry that there are bookshelves groaning with titles by bright people with PhDs saying how important conscious hiphop is. They get urgent attention. There’s nothing wrong with that, but they present only a partial picture. They’re mistaking volume for substance. Most people on the street realise that conscious hiphop doesn’t play much of a political role, but the intellectuals don’t. They think it’s still in the vanguard.”

The controversy adds a refreshing twist to a debate that has long been simmering within the African-American community. Bill Cosby, for instance, has declared war on rappers who, in his eyes, make a killing from degradation and violence. The trumpeter Wynton Marsalis is even more damning. “I call it ghetto minstrelsy,” he has said. “Old-school minstrels used to say they were ‘real darkies from the real plantation’. Hiphop substitutes the plantation for the streets. Now you have to say you’re from the streets, you shot some brothers, you went to jail. Rap has become a safari for people who get their thrills from watching African-American people debase themselves, men dressing in gold, calling themselves stupid names such as Ludacris and 50 Cent, spending money on expensive fluff, using language such as ‘bitch’ and ‘ho’ and ‘nigger’.”

Brave words. The problem with Marsalis’s assessment, however, is that the kind of retro-jazz he has championed in the past two decades is, bluntly, an overreverential facsimile of the music of 40 or 50 years ago. Although his restless campaigning on behalf of jazz has paid dividends in the creation of a splendid new performing base at the Lincoln Center, in New York, it is still not entirely clear whether the venue will ever amount to more than a museum for the well-heeled Manhattan middle class, black and white.

McWhorter’s comparatively measured approach may strike more of a chord with black listeners, although the fact that he is a senior fellow at the conservative Manhattan Institute means many people not familiar with his previous forays into politics (including the excellent polemic Losing the Race) will automatically write him off as a Republican hack. In fact, he is a centrist, and is supporting Obama in the presidential contest. (His Bloggingheads video dialogues with another independent-minded black intellectual, Glenn Loury, have been one of the most fascinating new media phenomena of this election year.)

In his previous books, McWhorter has bravely categorised the worst excesses of hiphop as a manifestation of “therapeutic alienation” - by which he means that they pander to a corrosive sense of victimisation. America, he insists, has moved far beyond the poisonous racial climate of the pre-civil-rights era. More controversially still, he believes racism is no longer the prime barrier to black progress. “Self-sabotage” is what concerns him most. Unlike Cosby, however, he hesitates before drawing a direct connection between rap’s most unsavoury manifestations and general levels of street violence. It is, he says, a stale argument, and one reason he thinks his book will annoy right-wingers almost as much as liberals.

What about the casual abuse of women embedded in so many rap lyrics? Again, McWhorter is cautious, perhaps excessively so. On the one hand, he has no problem reiterating his view that hiphop has produced “the most misogynistic music” in human history. On the other, he has yet to be convinced that the lyrics actually encourage violence. It is an exceedingly tricky balancing act.

McWhorter is much less shy about proclaiming his belief in an old-fashioned hierarchy of artistic values. Much as he enjoys the best examples of rap, he hesitates before placing most of them on the same level as the best black music of the 1960s and 1970s. Stevie Wonder’s socially charged album of 1973, Innervisions, remains one of his measures of R&B excellence.

A quarter of a century ago, McWhorter was intrigued by the advent of Grandmaster Flash, the pioneer rapper. Then disillusionment set in, as the next wave of practitioners slipped into bombast. Years later, he began listening seriously again, if only to try to connect with the all-pervasive music that was, for better or worse, shaping the tastes of the next generation in America and beyond.

At the pinnacle of McWhorter’s pantheon sit Brahms, Duke Ellington and Billy Strayhorn. In the end, he reaches for a gourmet analogy: “It’s like duck à l’orange and hot dog. Now, I love hot dogs, but sausage only takes you so far. To me, hiphop is like that. It’s great, but it’s not going to rise to the level of Porgy and Bess.”

All About the Beat: Why Hiphop Can’t Save Black America is published by Gotham Books

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