Consider the hare and the hyena. The hare, Clement of Alexandria told readers of his 2nd-century sexual self-help manual Paedagogus, was thought to possess both male and female sexes and swapped their roles from year to year. As for the hyena, it was believed to acquire an extra anus annually and ‘to make the worst use of these added orifices’, as Michel Foucault puts it in the newly translated fourth volume of his History of Sexuality.

For early church theologians the moral lesson was clear: we must not emulate gender-bending hares or randy hyenas. Rather, sex should be procreative, not pleasurable; we must go forth and multiply, borne by duty, not ecstasy. St Augustine went as far as to argue that since Adam and Eve were banished from Eden, sex was inherently tainted by association with original sin. Only outside Eden did Adam’s penis stir unbidden, cursing humans to become slaves to their degrading appetites. Many church fathers, Foucault considers, championed virginity as a lifestyle alternative.

All this is fascinating. But Foucault’s posthumously published book about sexual norms in early Christendom takes on poignant resonance, given claims earlier this year by a fellow French professor that its author was a paedophile rapist who had sex with Arab children while living in Tunisia in the late 1960s. If Foucault learned about the art of sexual restraint preached by the theologians he studied, Guy Sorman’s revelations suggest he rarely practised it.

Sorman told the Sunday Times that he witnessed Foucault throwing money at boys aged eight and inviting them to meet him for nocturnal sex at the local cemetery, where he abused them on the gravestones. The question of consent wasn’t even raised. Sorman, who gave the interview to publicise his book Mon dictionnaire du Bullshit — an indictment of irrationalist thought for which he thinks the likes of Foucault were responsible — said he regretted not telling the police, but that Foucault’s status as philosopher king made him fearful of doing so. He claimed that French newspapers were also aware of Foucault’s behaviour, but kept quiet. In this portrayal, Foucault figures as a Gallic Jimmy Savile, a predator hiding in plain sight, indulged by the Establishment. In Britain we defer to TV celebs; in France they abase themselves to intellectuals.

There are differences between Savile and Foucault. The latter indulged his libido abroad, in the time-honoured manner of white Frenchmen (Gauguin had sex with fetishised Tahitian women; Gide preyed on African boys). Moreover, while Savile now personifies evil, Foucault, who died of Aids in 1984, lives on as an influencer, like a highbrow, if dead, Kim Kardashian. Just as he had campaigned to reduce the age of consent to 13 in 1977, so today the women’s rights caucus of feminist groups, LGBT+ organisations and trade unions worldwide campaign for the abolition of ‘laws limiting legal capacity of adolescents … to provide consent to sex or sexual and reproductive health services’.

Liz Truss, the equalities minister, recently even blamed Foucault’s influence for illiteracy at her Leeds school, which seems a bit of a stretch. Her peers, apparently, were taught about sexism and racism but not how to read and write. Foucault’s ‘postmodernist philosophy’, Truss claimed, ‘puts societal power structures and labels ahead of individuals and their endeavours.’

This is unfair. Foucault’s early work was a sustained takedown of oppressive societal power structures. Madness and Civilisation (1961) and The Birth of the Clinic (1963) were histories of what the French call assujettissement — roughly, how we are dominated by institutional power. Discipline and Punish (1975) was a critique of 19th-century prisons, in which the Orwellian surveillance state was prefigured in Jeremy Bentham’s panopticon prison design. Foucault’s point in these books was that power is always with us — like the poor, only more so. With power, as with the hyena’s extra anus, what’s important is not what you have, but what you do with it. Truth, as well as what is right and wrong, is relative to what he called epistemes — underlying cultural codes that govern language, norms and values.

What’s more, Truss’s idea that Foucault preached against racism and sexism bears little scrutiny. Take sexism: in the first volume of The History of Sexuality (1976), Foucault wrote about a farm labourer who in 1867 sexually abused a young girl. The point of the story for Foucault was how power constructed from this incident someone deserving of punishment, making from ‘these inconsequential bucolic pleasures’ an ‘object not only of collective intolerance but of a judicial action’. Reading this again recently, I thought how much I’d like to have heard the young girl’s version. One person’s bucolic pleasure here reads very much like another’s rape.

But then Foucault was long a champion of liberating the libido from social norms. In 1971 he wrote the foreword to Anti-Oedipus, Gilles Deleuze and Félix Guattari’s eulogy to the revolutionary potential of not the proletariat, but desire. Like these fellow disenchanted soixante-huitards, Foucault junked the left’s abasement before Marx and Freud in favour of a new false secular idol: norm-free libidinal relativism. You don’t have to be Harvey Weinstein to buy into that philosophy, but it might help.

It is a short step from this fixation on desire, argue the authors of The Last Man Takes LSD — a fascinating study of Foucault’s American years — to dabbling in the then-current neoliberal thought which Foucault encountered while teaching in California in the 1970s. He liked the idea of busting down the welfare state, which he believed had created dependent, docile subjects. He heretically supported both the conservative French president Valéry Giscard d’Estaing and the Iranian revolution, while denouncing the dirigisme of the French communist and socialist parties. He had more in common with Thatcher and Reagan than Mitterrand. Maybe if Truss had read Foucault carefully she might have realised how much she shares with him.

Foucault was turned on by California’s cult of the self, whereby virtuosic individuals remake and remodel themselves beyond social norms and oppressive labels. That cult was French existentialism with an American free-market twist. The cult faithful the authors call ‘entrepreneurs of the self’. They suggest that by frequenting New York leather bars and San Francisco bath houses, and by dropping acid in Death Valley, Foucault became just such an entrepreneur, cultivating an image of himself as authentic and free to a world captivated by the pursuit of such delusions.

In the late 1970s, he also wrote the second and third volumes of the History of Sexuality, championing ancient Greek and Roman sex lives as antidotes to Christian shame and bourgeois repression. Critics pointed out that these erotic idylls were reserved for tiny elites; the sex lives of plebs, slaves, women and children were beyond Foucault’s remit. Ancient Greek slaves rarely write history —nor, I’ll bet, do pre-pubescent Arab boys get to tell their story.

All this makes the appearance of Confessions of the Flesh intriguing. The manuscript had been locked in a bank vault for 30 years, and whether Foucault would have wanted these now edited notes to see the light of day is uncertain. He told his literary executors he didn’t wish to become the Kafka to their Max Brod, but in a sense he has. No matter; it’s an undeniably fascinating text, since it deals with how our experience of sexuality has scarcely emerged from the long shadow cast by Augustine and other church fathers who preached the paradox that after the Fall sex was necessary yet shameful.

The book is readable and engaging, but the erotically blighting imperative to confess our sex lives to priests — and latterly to shrinks — arose in times beyond its compass. In any case, the book we really want to read is the one Foucault didn’t write — not a critical account of venerable Christian libidos, but his own.