What is a woman?
There was a time when a question like that wasn't seen as being all that hard to answer. A woman was simply a female member of the species homo sapiens, as determined by such things as physical biology and genetic makeup. Just as certain words and concepts were associated with the male of the species such as boy, man, son, brother, husband, father, grandfather, uncle and so on, so were some words associated with the female of the species such as girl, woman, daughter, sister, wife, mother, grandmother, aunt, and the like. While certain words and ideas did reflect societal constructs, such as "bachelor" for an unmarried man and "spinster" for an unmarried woman (with the idea that to be the first was no big deal while the second was practically a disgrace), the words I listed above had to do with relationships, and important ones. It seemed as though only yesterday people agreed that your brother could never become your sister, let alone your wife; now all it takes is for someone to shout "Love Wins!" for that horrible idea to become socially acceptable and those who object to it shouted down as irredeemable bigots.
I think that part of the problem is that in an age of modernity we have largely forgotten just how important the relationship-based words are, and the reason we have forgotten this is because we have forgotten what they mean. The vast majority of children born in China any time in the last several decades, for instance, have no experience whatsoever of "brother" or "sister" or even aunt, uncle, and cousin. In an America with a birthrate below replacement level and falling there are plenty of children who likewise will never really experience what those words mean on a deeply personal level.
And that's for "brother" and "sister," two words that indicate biological relationships. How much more are we forgetting what words like "husband" and "wife" mean, since so many people think a husband or a wife is just a temporary relationship dressed up to look better in public, and so many other people carry on like husbands and wives without bothering to marry? The beginning of the end of these ideas was no-fault divorce, which formed a couple of generations of people to think that husbands and wives were easily replaceable people primarily used for sex whose temporary role in one's life should not unduly burden one; the actual end, of course, was Obergefell, because once a husband became some sort of thing that could have another husband, or a wife the sort of thing that could have another wife, the words became completely meaningless to the level of gibberish.
The reason the concept of marriage is now gibberish is precisely because if marriage has nothing to do with sexual complementarity, that is, with the union of a man with a woman, then it has nothing to do with anything. All those other relationship words: mother/father, son or daughter, grandfather/grandmother, only have meaning and context within the light of that relationship of husband and wife. When we call an adopted child a son or a daughter, for example, we can only do that because we know what a son or a daughter is--in fact, the addition of the word "adopted" shows that we do understand what a son or daughter is, and that when we can raise someone else's child as a son or daughter this is a special gift both from us and from the child's birth parents who are, due to unfortunate circumstances, entrusting us with something so precious.
But when marriage no longer has anything to do with children, when biological sex gives way to fluid and fluctuating notions of gender that are grounded in nothing but subjectivity, when we can't say what a son or daughter is anymore because a daughter can have two "moms" and decide to become a son, then we can't say what woman is anymore, either (let alone a man). In the end, a woman isn't anything at all, except when she objects to the presence of "women with penises" in her gym's changing area and showers, at which point she becomes a bigot.
If women are nothing special, then mothers aren't, either. Already we see modern feminism going on the attack, floating the idea that women should be prohibited by law from being stay-at-home-moms once their youngest children are in school. After all, why should women stay at home to raise and nurture their own children, when they could be working ten to twelve hours a day building a career or at least selling stuff at the local big-box store? Women aren't the only ones who give birth anymore; plenty of "men" who just happen to have vaginas give birth too these days, so why should the women get to be slackers while the men have to earn paychecks, something that is far more important than bringing up the next generation of humans, or furries, or genderfluid fairy boi creatures with unicorn tattoos? Childcare should be outsourced to the cheapest possible workers so that women and "birthing men" can take a nice healing holiday after the birthing process and then get back to the widget factory as quickly as possible, so that the genders can finally be equal.
And if mothers aren't special, then neither are fathers (who can be born with either a penis or a vagina) or sons (who might have been inappropriately assigned the wrong gender at birth) or daughters (who face discrimination if they happen to be transitioning away from male) or aunts or uncles or grandfathers or grandmothers or pretty much anybody we used to refer to by those outdated relationship words.
What is a woman? The modern state answers, chillingly, "Whatever I say it is. And you must agree or face the consequences." And the modern men and women and genderless alternate reality beings cheer and proclaim that someone born a man is now the Woman of the Year...