Second part:
Now let’s start to address some of your points.
> "The whole point of female and male is to distinguish the two reproductive roles in sexually reproducing species, whether those are hermaphroditic or gonochoric. The sex binary is based on anisogamy, that is, two classes of gamete being of unequal size."
Yes, that's why "female" and "male" are useful abstract concepts specifically to help talk about reproduction in several species. Using these two terms, we can talk about a diverse spectrum of reproductive strategies, including hermaphroditic and gonochoric.
I think your argument breaks down to:
[1] The terms male and female are strictly to distinguish between gamete size in gonochoric species. [Already incorrect, but sure, that’s one possible definition we can use]
[2] Humans are a gonochoric species [yes]
[3] Therefore ALL humans are either male XOR female
Is this your argument? Because it can pretty quickly be disproven with one contradictory example: intersex humans exist. Deductively arguing from abstracts also means its application is quite limited. For example, it inherently assumes humans are reduced to their reproductive function, which is obviously false. If we’re purely arguing from the perspective of ability to reproduce, then do you have a larger category in mind for “sterile” humans, including infants, the elderly etc? Obviously not all humans are capable of reproduction, which is why it’s useful as an abstract, but that quickly falls apart once you look at concrete examples like individuals. Again, just because you CAN label everything in a binary way, it doesn’t actually mean that the underlying data is binary.
> To take one of your examples: a hirsute woman…
From your response, I don't think I was very clear with these examples. Let me see if I can make my points more clearly.
Every human has male and female aspects. If you look at one individual, how accurately could you predict certain characteristics about them?
If I say "this person has a beard," could you immediately say with 100% confidence that it was a "male"? No. You could probably guess with fairly high accuracy, about 90%, but you could not be 100% confident.
What I was hinting at with these examples is that there is no "necessary and sufficient" definitions of "male" and "female" for individuals where you can predict with 100% accuracy. It doesn't make anyone "more or less" of whatever sex they're categorized as, but these examples illustrate the complexity of the underlying system. The simple fact is that “male” and “female” labels aren’t always very predictive or relevant when being applied to individuals. Not every “male” has a penis or a prostate or is capable of reproduction, and not every “female” has a uterus, ovaries, or is otherwise capable of reproduction. Humans are more than their reproductive capabilities and simple labels such as "male" or "female" can't fully describe those aspects. Reproduction is not always relevant.
> Your comment about "drawing an arbitrary line" doesn't really fit with how biologists see this either…
Yes, when biologists are abstractly talking about reproduction, individual variation isn’t very relevant. They’re not even talking about sterile individuals. Broadly applying those types of generalizations to individuals isn’t helpful.
> Going way back upthread, this was originally about fairness in sport, male physiological advantage, …
You’re making several pretty big logic leaps in here. Let’s try to sort this out.
First, sport isn’t about reproduction. That’s irrelevant, so please stop trying to argue that gamete size has anything to do with sports. So why do we divide sports into "men" and "women" if reproduction isn't relevant? It's because you've correctly seen that sometimes there's physical, measurable differences between the two groups and we as a society want sports to have some aspect of "fairness." There’s a lot to unpack here, though and you’ve made several incorrect assumptions.
“Male physiological advantage” is an incorrect blanket assumption. Where is the “male physiological advantage” in sharp shooting? Olympic Skeet wasn’t separated by gender from 1968 until 1992, when Zhang Shan from China won the gold metal. After that it’s been divided by sex. Some sports are split by gender for different cultural reasons, and yes, in some sports men as a group tend to be much taller and have advantages in certain areas, but this isn’t as universal as you seem to think. Lots of transphobic people tend to focus on trans women in sports, but they’re dead silent on trans men doing fairly well in the Olympics. There are several examples in basketball, wrestling, swimming etc.
> he seemed to think there are medical interventions that can be performed on humans that convert males to female, which is not the case
There is so much variation in human sexual development, as discussed with intersex, that there honestly doesn’t need to be much “medical intervention.” There is a lot of overlap between the sexes, and the fact that it’s actually so hard to define a criteria to separate them, makes this all easy to understand. And that’s where gender comes in. Gender itself is largely a social construct, so we’re pretty flexible on how we define it. Basically it’s pretty easy to see that it’s a real phenomenon and as scientists, we would like to document and discuss this real phenomenon.
> Then you commented stating that sex is a spectrum. This is typically introduced into an argument to try to bolster the claim that it is possible for humans to change sex, …
Sexual development in humans is hopefully by this point fairly obviously a spectrum. Human intersex exists in many different forms. In general, sports have nothing to do with reproduction, so that’s largely irrelevant. However, we as a society would like to make playing sports generally “fair” and there are general, measurable differences between men and women, and yes, sometimes that does mean men have a physiological advantage over women in certain sports. Scientists have already looked into this, and they determined that after 2 years of hormone therapy transwomen are fairly hard to distinguish from the natural variation in ciswomen for all their metric. That’s why there have been rules in place. I’m actually not sure what the rules are for transmen, but the fact that they’re showing up to the Olympics means that they’re probably doing okay.
> So that leads into another issue of why this "sex is a spectrum" idea has been introduced to the world at large. …
Hopefully you have a better understanding of what I mean now. You’re literally using the terms as a spectrum by talking about intersex and using it to describe hermaphrodite species. Being able to apply binary labels to a system doesn’t make it “binary,” what actually matters is the criteria and the output when we’re talking about models. Does that make sense? By calling it a “spectrum,” I’m not actually introducing some new niche model, the fact that I referenced a textbook should make this clear, I’m just saying the data isn’t “binary” and that should be obvious alone from being able to describe so many different species with two terms.
Hope this clears things up!