On Friday, two sisters who used to work as personal assistants to Nigella Lawson were cleared of defrauding the chef and her ex-husband Charles Saatchi of £685,000. Since they had claimed that Ms Lawson allowed their extraordinary credit-card use because they kept her habitual use of cocaine quiet, it was immediately suggested that the verdict had left her reputation in tatters. The claims against her, the Daily Mail said, "shatter the squeaky clean image of one of Britain's best-loved TV chefs". The problem for Nigella, by this account, is that her alleged addiction – which, whatever anyone infers, the jury was not actually asked to provide an opinion on – is so heinous that no one would trust her as a dreamer-up of luxurious cakes. "Publishers and television companies in Britain and the US," the Daily Mail regretfully noted, would be bound to "consider their association with a 'brand' tainted by such damaging allegations".

Meanwhile, in another London courtroom, Tulisa Contostavlos was denying the claim that she had arranged an £800 deal for the same devil drug. She dressed smartly for the occasion and failed to smile for the cameras, and so, understandably, The Sun headlined her as NIGELLA MARK TU, appending the charming qualification: (in her dreams!). The accusation Tulisa faces arises, funnily enough, from an elaborate sting organised by The Sun itself. In June, it published a story telling how three of its journalists, including the investigative reporter Mazher Mahmood, made repeated contact with her in the guise of film producers, and eventually asked her if she knew anyone who could get them any cocaine.

And then there's R Kelly. You know R Kelly, of course: he's the pied piper of R&B, a 50-million-album-selling star of almost unmatched popularity, a huge name on both sides of the Atlantic. Although he's an accomplished balladeer, his most acclaimed work has a tendency to the extravagantly horny: not for nothing did The Independent, last year, describe him as "the most irrepressibly lubricious of contemporary soul singers".

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That review is indicative of a general mainstream engagement with his work, and sense of amusement at his sexually voracious persona. The Guardian riffed on the title of his "hip-hopera" with "Trapped in the Closet" to suggest that items secreted in his own cupboard include "chocolate-flavoured lube"; the feminist blog Jezebel sees something funny in the way he "winds his musical threads on his freaky sex loom". The NME, when warmly reviewing a song called "Feelin' Single" last year, chortlingly warned its readers to "lock up anything with a pulse!" because "the Kelster … is on the prowl".

When considering this sort of verdict, there is one more piece of useful context to remember, one which may have slipped your mind: R Kelly has settled a series of lawsuits brought by underage girls who have accused him of raping them. He has faced trial for – and been acquitted of – child abuses charges, after filming himself having sex with, and urinating on, an underage girl. He married the precocious singer Aaliyah when she was 15 years old, and he was 27. And all of this has been true, and in the public domain, for years. But most of the time, most of us have chosen to look the other way. Our attitudes could perhaps best be summed up by that NME reviewer's conclusion. "Cause for concern?" he asked. "Not when the result is a slice of sleek and delectable sunshine soul."

Last week, something changed: we were given another nudge to look back in the necessary direction. After years of fighting a lonely battle reporting on the subject, a music critic for the Chicago Sun Times, Jim DeRogatis, agreed to an interview with the Village Voice. In it, he detailed the dozens of interviews he has conducted with women and girls who accuse Kelly of varying degrees of harassment, and expressed his deep frustration at the failure of other branches of the media to take up the story.

All of this prompted a slew of outrage, and a self-conscious reconsideration by many of those who had joshingly dispensed with the allegations against "the Kelster" before launching into another paean to the singer's sensational vocal range. (For what it's worth, I'm no exception to the general failure: I never tried to flesh out my hazy awareness of the allegations, often hollered along to "Ignition" at parties, and never, in several years as an editor, thought to ask a reporter to look into Kelly's behaviour.) Why, everyone wondered, have we been ignoring this for so long? DeRogatis knows what he thinks: "The saddest fact I've learnt is nobody matters less to our society than young black women. Nobody."

It is important to say that no court has found Kelly guilty of a crime. When he faced those child pornography charges, his lawyers – against their own evident expectation, according to reporters in the room when the verdict was read out – persuaded the jury that an unnamed person might have spent months meticulously doctoring the tape so that their client's head was convincingly grafted onto someone else's body.

So if criminal guilt is the only thing that can mark someone out as unworthy of our attentions, fine. Let R carry on crooning. But in other circumstances, the standard of proof we require to consider someone's reputation to be damaged appears to fall some way short of "beyond reasonable doubt". Let's review. In the Nigella case, the necessary standard for reputational damage is the claim by someone accused of defrauding her that she had a coke problem. In the R Kelly case, the necessary standard is not quite defined. But things that do not meet it include: marriage certificates proving that someone falsified Aaliyah's age so that a judge would allow the two to marry. Scores of allegations from women who independently came forward to accuse him. And court documents that describe some of these claims in forensic detail.

This reputational confusion is not surprising. But it is repellent, and it is sexist. The obscure underage girls who accused R Kelly and the famous adult women accused by the tabloids are subjected to the same assumption: that they are jezebels, projectors of a squeaky-clean image who harbour a secret darkness. Even after Savile, if a child says she was raped by a star, we think she must have wanted it; even in 2013, if a woman sells homely food and privately takes an illegal drug, we construct a contradiction that would never seem strange in a man.

For all the online revulsion, I don't suppose that Kelly will suddenly be shunned. His new album, Black Panties, with a cover showing the middle-aged star mobbed by nearly naked young women, one of whom appears to be about to give him oral sex – has enjoyed a warm critical reception. It features tracks entitled "All The Way", "Crazy Sex", and "Marry The Pussy", and has already sold 133,000 copies in the United States alone. It will presumably do well in the UK, too. The Sun has enjoyed itself with the album's publicity drive, reporting on "R Kelly's pants-in-CD twist" whereby the deluxe version of the CD comes with a pair of lace knickers. It would be foolish, we are told, to accuse Kelly of "advertising what he can't deliver".

As for Kelly: he has a straightforward response to those who think his history should give people pause before buying his music. "As long as I got fans screaming my name, buying my records, and supporting R Kelly," he says, "everybody who doesn't agree should listen to the last song on Black Panties." To put it another way: I am famous, and so my reputation should be impervious. The claims that are made against me should count for nothing, and the people who make them should not be heard.

The title of the last song on Black Panties, by the way, is "Shut Up".