Couple of pages behind so this might have been said but booboo -
conforming to the function of man: there are two versions of this argument. The simplistic one sets whatever the speaker wants to promote as the function of the species thus prejudging the conclusion and making the argument circular e.g. the function of humans is to procreate, any sexual act that doesn't lead to procreation does not fulfill the function so is diseased.
If humans can be said to have a function then it is to procreate. It can't really be called a function though because there's no purpose in it. Humans don't have a function, we just are. And we are because every generation of our ancestors have procreated successfully right back to the beginnings of life.
A natural variation (like red hair) is something that can be passed on without affecting the viability or reproductive capacity of the organism (at least not to the extent that its competitors outbreed it).
Intersex people are usually infertile. They can't pass their condition on as a natural variation. Intersex conditions are not natural variations they are developmental disorders which affect reproductive capacity.
BTW, what is simplistic is thinking that sexual acts have only a reproductive function. We're social apes. Sex is for babies but also for pair and group bonding, among other social functions.
Intersex people are not in any way clearly harmed by being intersex
This isn't true. Infertility is very distressing for lots of people. Additionally, some intersex conditions have wider effects. Klinefelter syndrome, for example, can cause poor muscle tone, difficulties with coordination, language and literacy and possibly decreased life expectancy.
That's not even touching on the social and psychological issues of trying to navigate an extremely gendered world with an indefinitely sexed body.
Intersex and trans are two totally different things. Trans people have totally normal male or female bodies before they take hormones or have surgery.
I hate the way intersex people's experiences are being co-opted by the trans debate. I was thinking earlier though, all the rights trans people are demanding - self-identification, access to the sex segregated spaces they feel are most appropriate, changed documentation and records ... On the whole I have no problem with these rights for intersex people*. They are the group who have been 'assigned at birth', they are the group who do actually need to 'identify' as something, because their sex is not obvious or unambiguous.
*Not sure how I'd feel about an intersex person who had apparently lived comfortably as male their whole life suddenly identifying as female.
You mentioned schizophrenia and bipolar in an earlier post too and questioned whether these might just be normal human variations. No. They are distressing psychological conditions which severely affect a person's ability to lead a normal life if left untreated.