You might think that in an art world that encompasses the Chapman brothers' phallus-nosed children and Jeff Koons' lascivious studies of La Cicciolina (sample title: "Dirty Jeff On Top"), you would have to sweat blood to produce a work so offensively sexual it would be ejected from a top London gallery. This, however, was the fate meted out to Leena McCall's Portrait of Ms Ruby May, Standing, which was removed from the Society of Women Artists' 153rd annual exhibition at the Mall Galleries after being deemed "disgusting" and "pornographic", according to the artist.

When I tracked down the painting online I was so flummoxed as to the likely cause of disgust that I thought it must be the fact Ms May was depicted smoking a pipe. Few things cause more umbrage now than someone wantonly enjoying tobacco. But further investigation revealed it was the way the sitter's short waistcoat and undone breeches framed a luxuriant dark V of pubic hair – not to mention, the "Come hither, if you dare!" expression on May's face, as she coolly scrutinises the viewer – that seemed to be the problem. The painting smacks of Isherwood's Berlin with its cabaret noir sensibility: Ruby May is a demi-clad femme fatale in pantomime boy's clothing, channelling Liza Minnelli and EF Benson's Quaint Irene – as alluring to women as she is to men. You can just about see how it might épater la bourgeoisie, without feeling for a second any outrage is justified.

The Mall Galleries have issued the following statement: "As an educational arts charity, the federation has a responsibility to its trustees and to the children and vulnerable adults who use its galleries and learning centre. After a number of complaints regarding the depiction of the subject and taking account of its location en route for children to our learning centre, we requested the painting was removed."

You can't help wondering if the affronted viewers frequenting Mall Galleries have ever sauntered over to the National Gallery, where Bronzino's erotically charged Allegory with Cupid and Venus (showing the boy archer fondling the naked goddess's breast) is on display to visiting school parties; or whether they feel the Tate should dispose of Sir Stanley Spencer's Double Nude Portrait, with its unsparing depiction of the artist's flaccid penis and his wife's hirsute mons pubis.

Mind you, the Society of Women Artists was permitted to replace McCall's work with another less provocative nude: one where the model wasn't tattooed and standing hand-on-hip, all unbuttoned. It seems the Mall Galleries' clientele can cope with nudes, so long as the model is a more passive and unthreatening recipient of the wandering viewer's gaze. Which all seems a desperately outmoded form of prudishness, like the wartime strippers at London's Windmill club who were allowed to pose naked, by the Lord Chamberlain's reluctant acquiescence, so long as they didn't move. They posed with one foot forward, obscuring any glimpse of "the fork" (ie vulva). The implication's clear: the minute a woman is alive and free to move, an active agent of her own sexuality, she is a menace to society.

McCall is understandably incensed at the censoring of her portrait, as her avowed intention in painting it was to explore, "how women choose to express their sexual identity beyond the male gaze". It's an added irony that her work should be removed from an all-female exhibition, curated by women. When I contacted the artist via her website, McCall explained that Ruby May (who leads erotic workshops) had proudly wanted to own the pubic hair that is so often waxed, covered or air-brushed away in contemporary depictions of the female body – and rarely glimpsed in classical ones, come to that. The painter can't begin to understand how a painting that reveals no intimate flesh, other than the pelvic triangle, could possibly be described as pornography.

My sympathies are entirely with McCall, who has launched a Twitter campaign asking supporters to contact @mallgalleries using hash-tag #eroticcensorship. It seems retrogressive, bordering on insane, that any corner of the art crowd should view a lush lady-garden as offensive at a time when celebs such as Gwyneth Paltrow talk about sporting a 70s vibe, while the writer Caitlin Moran writes about "finger-combing" her "Wookiee". You could even argue that non-depilated representations of the female body are precisely what school children should be seeing, so they understand body hair is normal and, yes, desirable.

You wonder if the cross-legged Puritans responsible for defenestrating the portrait have ever seen Gustave Courbet's L'Origine du Monde at the Musée d'Orsay, with its splendid sprawl of black-haired vulva. After all, Courbet's carnal canvas does not include a challenging female face to bring the sitter alive, or challenge the viewer.

• Update 8 July 2014: The SWA said it selected the painting during the submissions process for its annual open exhibition. The executive secretary, Rebecca Cotton, said: "We thought the painting was beautifully executed and the composition was much admired. We saw nothing wrong with it; had we, the piece would not have been selected. We hire the gallery space from the Mall Galleries for the period that the show is on. The gallery took it down without seeking our approval."