In photographs, Erika Leonard (EL James) appears dependable and blameless, like a deputy head of a girls' school who quite likes M&S floral dresses. Looks lie. With Fifty Shades of Grey, this erstwhile TV executive has cannily exploited "post-feminist" confusion and sexual restiveness in a period of plenty. I bought the book to see what made it so irresistible to so many.

The narrative is so corny you couldn't caricature it, and the S&M bits are grubby and foul. In sum, an Eng Lit student in Seattle, a virgin (yes, really) meets a heart-stoppingly handsome millionaire, swoons, and allows herself to be taken into his "red room of pain" to be punished and enslaved – for, I assume, being a woman. I was not titillated. I didn't long to be bound and gagged and thrashed for "love". I washed my hands with anti-bacterial soap, but couldn't cleanse my mind of rising rage and desolation.

James has sheathed hard porn in a soft summer wrap, sold fantasies of sexual subjugation to vacuous yummie mummies and middle-class female singletons who are clueless about its implications. Living comfortable lives, they must pursue vicarious excitement by reading about pain, and playing at it in their bedrooms. Sales of bondage equipment have shot up since the book came out.

OK, I hear all you fans of the book yelling at me. I have no business prying into people's motivations and chastising them for the sexual games they choose to play. Yes, agreed. But the phenomenal spread of this bonk-buster takes it out of that intimate space and should make us think about the social and political landscape, the victories and failures of feminism, and the dissonance between female equality achieved and equality willingly surrendered by females.

What prayers is this manipulative, horrible book answering? What does it say about life for young women in our times? And the men too? Bret Easton Ellis shot to fame with his graphic novel American Psycho, about a serial killer who mutilated his female victims. Feminists denounced the novel, which they said was a "how to" manual for such violators. Now, creepily, Ellis is keen on getting Fifty Shades of Grey made into a film. I have talked to men who say, with disturbing certainty, that sales of this book show what women really want. One of the most foolish assumptions of modern life is that everyone understands that fantasy cannot affect, colour or distort the way we actually live and behave. It absolutely can and does.

Another S&M book that has sold millions of copies is The Story of O, first published in 1954. The author was a Frenchwoman, using the pseudonym, Pauline Réage. You can see why it took off in the period when post-war female emancipation was being pushed back and women were expected to go back into the home, rediscover the "pleasures" of serving men, and suffering happily for love.

Today's western societies couldn't be more different. Women and girls expect to get the same chances and successes of men. Not that most do, but that is the expectation. Greater sharing of domestic chores, money to pay for childcare, empathetic employers and legal parity have given women better lives than ever. And yet internal traumas and guilt, low self-esteem and inchoate fears still deny females real confidence and ease. High-fliers often have no luck with men. Others have babies, flee the workplace and turn into wifies, because it is so damned hard doing it all. Even more alarmingly, evidence is emerging of young women, including teens, putting up with physical and mental violence from their boyfriends. The US TV series Girls runs storylines which normalise the idea that some boyfriends get off on owning and beating their partners.

Katie Roiphe, a New York academic and columnist, writes intelligently about this modern female condition. She wonders why free will is such a burden for 21st-century women, why in some spheres they so readily surrender to macho power. Could it be that equality is too much responsibility, or even that its imperatives can be boring? Maybe.

There are, I think, darker reasons. When young women become instinctively assertive and free of gender constrictions, their liberty threatens the "natural" order. So they have to be reminded of their place, taught they can never be good enough and must relearn submission.

I have been shocked recently to discover how regularly female university students have their drinks spiked so they can then be raped. Sex is freely available but what these men want is humiliation and savage domination. Fifty Shades of Grey reinforces those sexual dynamics, and gives the message that even educated women can only be fulfilled if entrapped and tortured by rich and powerful men – that abused victims ask for it and love their abusers.