Less than three weeks ago, Dominique Strauss-Kahn sat down in a Paris restaurant for an off-the-record lunch with two journalists from the daily Libération. The IMF chief outlined the three biggest personal hurdles in his relentless campaign to become president of France: "Money, women and being a Jew."

He started with women. "Yes I like women, so what?" he asked. "For years, there's been talk of photos of a giant orgy, but I've never seen them come out," he added, challenging his opponents to produce long-rumoured pictures of a night at a posh swingers' club dating back decades. He said he had warned President Nicolas Sarkozy (while they stood side by side at the urinals of the gents during a recent international summit) to stop smearing him over his private life. Strauss-Kahn then volunteered to the journalists a hypothetical example of something that could bring him down: "A woman raped in a parking lot who is promised half a million euros to make up her story."

Before Strauss-Kahn's opponents began throwing what one socialist described as "stink bombs" at him, he was keen to present himself as the victim of a potentially ruthless campaign.

Everyone in French political and media circles knew Strauss-Kahn's achilles heel was his attitude to women. Even his closest political allies admitted he was an inveterate seducer, an unashamed libertine. But what makes the scandal new and unprecedented in a presidential race is the crossing of the line to sexual violence, attempted rape and brutal assault.

Strauss-Kahn denies the charges, and his allies call him a seducer without the "profile of a rapist". But if, as the extreme-right Marine Le Pen affirms, all of Paris had long been abuzz with talk of his "rather pathological relationship" with women, why wasn't Strauss-Kahn pulled up on it before in France? He had already been chastised by the IMF over one affair with a junior in 2008.

It raises the uncomfortable question in the French media and politics of two parallel worlds: what is printed, and what is behind it, gossip, and what must officially remain "unsaid".

Consensual extramarital sex is a non-story in France, part of the right to a private life protected by fearsome libel and privacy laws. Having a mistress, philandering, even routinely propositioning journalists have been brushed aside for countless political figures. "How many senior male French politicians aren't either a groper, a cheater, a charmer or a serial seducer? And it goes right to the top of the political class," sighed one news editor. "France is still a kind of monarchy that kept the aristocratic morals of the 18th century. The lord of the manor has a right to the women; the king has his mistresses." If more allegations against Strauss-Kahn come to light and lead to criminal charges, it will call into question a taboo in France about speaking out.

Tristane Banon, the novelist and journalist is, according to her lawyer, preparing to go to police alleging Strauss-Kahn sexually assaulted her in 2002. Her mother, Anne Mansouret, a senior Socialist figure, said that she advised her daughter not to file a lawsuit at the time because Strauss-Kahn was a politician with a bright future, as well as a friend of the family. But she said that even the fact that her daughter later spoke out publicly about the attack on TV had left her "traumatised" by the subsequent "harassment" in her professional life over having dared to speak out.

Her mother suggested there was a kind of "invisible barrier" put up on her work projects, as if media bosses and publishers feared the consequences of "what she could reveal". Strauss-Kahn's spokesman has previously denied the claim, and said Banon had invented the allegation to generate publicity for herself.

The journalists, Christophe Deloire and Christophe Dubois, broke a taboo in their 2006 book, Sexus Politicus, about politicians' sexual behaviour. They wrote of Strauss-Kahn's tendency to "seduction to the point of obsession", mentioning, but not naming, female journalists who had been irritated by his gestures towards them. They also referred to one senior civil servant who didn't take up his offer to "come up to his office to relax".

It seemed striking that when Strauss-Kahn left for the IMF in Washington in 2007, with many politicians privately wondering how he would cope in a puritan US which frowns upon sexual advances, only one journalist raised the issue. Brussels correspondent for Libération, Jean Quatremer, wrote on his blog: "Strauss-Kahn's only real problem is his relationship to women. Too heavy … it borderlines harassment." Strauss-Kahn's communications team asked him to take the blog down. Quatremer explained to Le Parisien that he had refused, saying if they thought it was libellous, they could sue. They did not.

In 2008, the French press began to more openly touch on the issue of Strauss-Kahn and women after the IMF investigated his affair with a junior colleague, the Hungarian economist Piroska Nagy. He was cleared of abusing his position but was forced to apologise. Nagy said she thought he had a "problem" which affected his ability to work with women. Others in France spoke out. The Socialist party MP Aurelie Filipetti recalled a "very heavy, very pressing" come-on to her by Strauss-Kahn. She said that afterwards: "I made sure I never ended up alone with him in a closed space."

The humorist Stephane Guillon went furthest in 2009, satirising Strauss-Kahn's "obsession with females" on the equivalent of Radio 4's Today programme. Strauss-Kahn accused him on air of "nastiness" and Guillon – already under fire for lampooning several political figures – was sacked shortly afterwards.

In 2006, when Strauss-Kahn failed in his bid to become the Socialist presidential candidate, part of his problem was his publicly haughty and condescending attitude to the eventual winner, Ségolène Royal.

But five years later, as Strauss-Kahn's opinion poll ratings soared and he was tipped to become president, it was clear that a saga like the Nagy affair had no effect on the electorate's view. Sexual violence is another matter entirely. In a country where the leader's sexual habits are officially ignored, allegations of attempted rape have been a severe shock.