This was in reference to Champion of the Rose, where I'd built a 'bi-normative' world. The story did not touch on the terrible discrimination and pain that non-heterosexual people regularly face in our own world - the protagonist never discusses or even thinks about her sexuality. Characters are shown in a range of situations - committed m/f or f/f relationships, disappointed in or longing for past relationships, or happily flitting from lover to lover, guided only by opportunity and personal taste. I also built into that world the concept of 'thirds' and 'tribonds' to handle different ways society would expect same-sex people to approach conceiving children. But this was just in the background: never underlined or directly examined. Zero difference worldbuilding involves making massive changes to a status quo imbalance, and presenting it without remark.
In almost all of my books I do exactly the same thing with the role of women. The Darest, Eferum, Touchstone and Medair books have no societal sexism (though individuals are free to be asses). Women have the same inheritance rights, rights to own property, right to rule, and to pursue careers, as anyone else. I don't discuss how this came about, or how awesome it is: it just is a fact of the world, like gravity.
There are a few reasons I build 'zero difference' worlds, but a primary one is to move away from the limitations of stories I have already read.
I Can So Do ItI have long sought stories of "girls doing stuff". Often, the books I cheerfully gulped down were "girls can too" stories. A girl in a sexist society is forbidden from doing something, and wins through adversity to stand triumphant (often assuming and discarding a boyish disguise) having saved the colony/won the battle/defeated the Dark Lord AS A GIRL! (*gasp*)
These stories are a lot of fun. Hunting, one of my earlier novels (in order of writing), is set in a structurally sexist kingdom (somewhat isolated from a wider world without such inequality), but I put her in boy's clothing specifically to avoid time spent telling the protagonist Girls Can't Do That. I've loved many a story of girls proving that they Can So Do It, but at the same time Hunting is my only book where I've even touched on that dynamic because the world itself limits how you tell your story.
Even if you allow your main female character to Do Stuff in a structurally sexist world (by putting her in boy's clothes, or giving her a Get Out of Gender-Jail Free card, or showing her valiantly Doing "Women's Stuff" because Women's Stuff is Also Important, by setting the story in a structurally sexist world, the story often revolves around and repeatedly has to deal with gender limitations.
An (unmarried) girl in such a world is unlikely to be sexually experienced, which considerably changes her dynamic in romances. Tasks such as investigation are endlessly complicated when a woman would cause comment or scandal simply by her presence at, say, a race course or a public tavern. A woman's expertise and suggestions are likely to be dismissed in worlds where they are held incapable of non-domestic skills.
And the 'cost' to the story is time. Time devoted to overcoming the problem of being female in order to tackle the problem that is the plot.
It's not easy beingOf course, sometimes the plot is primarily about being female. Books that directly examine and hold up to the light challenges faced by women (or people of colour, non-cis people, non-het or differently-abled people) are incredibly important. Many readers find it a gift and a direct aid to witness a character in a book struggle with the same issues that are a central concern of the reader's daily life.
The character(s) might overcome those challenges, test different methods of tackling them, or be injured and retreat from them. The importance is in the acknowledgement, on shining a light on both the dystopian-level oppressions and the small, silent shames that are delivered to people who are not sitting on the very top of the privilege pyramid.
My particular interest as an author, however, is not holding up a mirror, but creating a window to somewhere else.
Second 'Verse, Same as the FirstI've walked through thousands of fantasy worlds. There have been some very unlike our own, but the vast majority are more than familiar. Even if there are gods who can enforce their edicts, even if physics is debatable and magic a wild card altering all manner of expectation, these massive variances seem to make little difference to culture. Humans are divided into women who are domestic and men who are in charge. Heterosexuality is not only common, but mandated, with transgression punishable by law. Civilisation seems inextricably linked to a low melanin count.
At times when reading I feel as if stories are trying to lace us into a corset of "this is how it is" and refusing to let us breathe. We are being told over and over that some things are inevitable. Not only are they inevitable, but they are the primary aspect of our Selves, and to be x or y or z means that we must absolutely, inescapably devote large amounts of time to dealing with mandatory hate.
Loosening the staysSo one of the reasons I both seek out and write "zero difference" worlds is simply to breathe. To not shower my characters with major threats and micro-aggressions, to not make prejudice against that character their one abiding truth, their constant preoccupation, and the required focus of the plot. To show that a person can simply be x or y or z, and also a and b and c, while focusing the majority of character time and energy on j.
With me 'j' is usually the morality of mages, or dissonance caused by time dislocation, or bonds of rule or friendship, with a side order of frustrated artist. And I want to put my characters through those questions, not set them on the old, familiar treadmill of "girls can't do that".
Modelling possibilityAnother reason I enjoy "zero difference" worlds is to take a next step. In the Darest books, I began to explore what social constructs would develop in a bi-normative world. In the Singularity Game series I'm questioning gender by introducing virtual body-hopping. In the Trifold Age books I hamstrung colonialism - the period of European invasion on the back of gunpowder and disease - by introducing gods who "Answered" and protected their various peoples.
That is not to say that zero difference worlds are Pollyanna wishful thinking. Hamstringing a few invasions, of course, won't necessarily stop people from hating, fearing or demonising other races, any more than interventionist gods necessarily erase institutional sexism - Gods, after all, can be racist and sexist too. But limiting colonialism can be used to fiercely undercut the terrible lie that is the White Superiority narrative. Changes such as this allow me to look into a world where the myriad African kingdoms whose names we're never even taught in school were not dismantled to the point where people deny they ever existed. Where English is not a dominant language, and the influence of the Egyptian social imperative of Ma'at directly opposes the concept of 'serf'.
Because one of the real joys and pleasures of a zero difference world is not treating what we have now as inevitable, true, and correct. There is room for more worlds than that.