Raise a bumper of Baileys Irish cream, please, to a victory for affirmative action. Aged almost 18, the UK's first women's fiction prize appears to have made itself redundant. Launching the – then – Orange, now Baileys women's prize for fiction, in 1996, the chair of the judges, Kate Mosse, explained its inspiration: the 1991 all-male Booker shortlist.

Although, in 1995, Kate Atkinson and Pat Barker had, respectively, won the Whitbread and Booker, the big prizes were perceived as "intrinsically male". "Most women don't find their way on to shortlists and even fewer actually win," Mosse said. "Just imagine what people would say if the Booker released a shortlist with only women. Everyone would see it as an enormous political statement."

Well, not everyone, now that the Costa, also up there in the premier prize league, has announced an all-women fiction shortlist for this year, a line-up that nobody seems to think is anything other than a literary statement. Rather, further evidence of unprejudiced prize-giving has turned attention back to the Orange/Baileys prize and its objective in a world that no longer contains Auberon Waugh and Kingsley Amis, whose opposition reportedly cost Mosse her first sponsor. "One can hardly take the winner of this seriously," Amis said.

And when the first year's Orange judges dismissed Penelope Fitzgerald's sublime The Blue Flower, along with Pat Barker's The Ghost Road, while at the same time complaining that the submissions were "parochial, small-minded and inward-looking", even Orange sympathisers could see his point. On the other hand, when the prize rewards acknowledged talents, already honoured by an establishment it may have helped to make more enlightened, what primary purpose, other than the promotion of Baileys Irish Cream, is being served? But these arguments have gone on since AS Byatt suggested that the 1991 Booker shortlist was, in fact, innocent. "My opinion is that for the last 10 years or so it is observable that there have not been as many good women writers as men."

Unlike Amis and a number of equally useful white male successors, eminent female critics could never be cited by the Orange prize as part of the problem. What could Orange say to Anita Brookner and AS Byatt, both of whom have both refused to have their work submitted to what the latter described as a "sheep pen"? Only, perhaps, that if the Orange is indeed sexist, a ghetto and, in its divisive focus on sexual identity, an almost absurd contradiction of fiction's imaginative purpose, it is still a fantastic thing to win. As Cynthia Ozick wrote in 2012, when she contemplated the difficulty, for an Orange-sceptic, of finding herself shortlisted: "Where now were my anti-separatist convictions?" In the event, she was exhilarated. "It came to me then, since a writer is a writer is a writer ('male and female created He them'), it may also be true, for the sake of literature itself, that a prize is a prize is a prize."

In that instance, it was won by Madeline Miller for The Song of Achilles, in Orange's final year as sponsor. The chair of the judges, Joanna Trollope, confirmed – for the benefit of anyone who had missed contributions from Margaret Atwood, AS Byatt, Annie Proulx, Beryl Bainbridge, Hilary Mantel, Sarah Waters, Jeanette Winterson and others – that female subject matter had come on in strides. "I hope the breadth and adventurousness of the settings and the subject matter puts to bed for ever the idea that women only write about domestic things." If so, that was another rationale gone. Should the prize have just congratulated itself, in 2012, on a job well done and welcomed men – and AS Byatt – possibly with an all-women panel of judges such as France's Prix Femina, drawn from the inexplicably underemployed pool of women reviewers? Certainly, the remaining case for Orange's discrimination – that it helps lesser-known women writers – looks like a rather slender case for eternal affirmative action, once the offending culture has reformed to the point of an all-female Costa shortlist. Even revolutionaries at the EU, countering the entrenched exclusion of women from business, propose that a temporary quota system should end in 2028.

In fairness, without their adherence to first principles, supporters of the Orange might never have attracted a sponsor as eminent as Baileys, whose makers have, by a stroke of luck, decided women might be more promising garglers of the stuff. Anyone who missed a cinema ad in which a glass of Baileys gloop is transformed into scores of shimmying beauties, so as "to celebrate the spirit of modern womanhood", can still catch its festive promotion, "spend time with the girls this Christmas", in which three modern women, discovering that they prefer the beverage to any amount of testosterone, illustrate how positive action can be cute and fun.

Baileys' targeting of this sickly drink is, in short, as condescending to women as the tweediest literary cove in 1996, to the point, surely, that the sponsorship makes a nonsense of the original prize – unless you thought it was nonsensical to begin with. Baileys, wrote the novelist Jenny Diski, is "a perfect sponsor for a demeaning fiction prize". With respect, I still feel Bic for Her would have been the more elegant fit.

But Orange's work is done and how brilliant it would be, Baileys notwithstanding, if other equality campaigners could achieve something approaching that level of acceptance for positive discrimination, in less glamorous trades. If literature no longer needs or never actually needed Byatt's "sheep pens" to protect individuals who would not otherwise get a look in, the recognition of women in politics and business still proceeds at a pace that promises parity not just long after this columnist's death, but after her daughter's, if then.

Yet, while the men-excluding prize is associated – at least by Baileys – with celebration, and described by one supporter, Martha Lane Fox, as "joyous, glamorous, high profile", affirmative action anywhere else is continually denounced as demeaning and out of the question, often by influential, nominally feminist women, competing to see who can sound most like Kingsley Amis or, to be more accurate, Robert Southey, when he told Charlotte Brontë to put a sock in it ("Literature cannot be the business of a woman's life").

The new EU proposal for temporary boardroom quotas has been criticised by the City CEO Helena Morrissey, notionally a top diversity enthusiast, as "patronising to women". Tory women, barely audible in the roar of Etonians, have the identical problem with all-women shortlists.

In the circumstances, male loyalty to the status quo can be unstintingly expressed, not only by Ukip neanderthals, citing female baby hunger as a reason for their otherwise inexplicable visibility, but by resentful Labour committees, reacting to all-women shortlists with "open" lists composed entirely of men, and by David Cameron, who still struggles to compute that marriage to Mrs Cameron is not an example of affirmative action. It is at moments like this that the modern woman reaches out, with trembling hands, for the comfort that only comes from a bottle of Baileys Irish Cream, the positive discrimination choice.