> The science of basic human biology is now a “regressive opinion.” Stunning.
Your lack of medical knowledge is just as stunning.
Not only does intersex exist (yes, humans can indeed have both primary sexual organs, though it's rare), there's also a plethora of conditions that blur the line, from De la Chapelle-Syndrom to Swyer-Syndrom. There's chromosomal-, gonadal-, hormonal-, and anatomical variations that are part of "basic human biology" yet result in individuals that cannot easily be classified by vagina=woman and penis=man.
I've seen this argument a few times, but I don't think it holds up
The majority of trans people have/had functioning genitalia. Gender identity isn't restricted to the set of people outside the crudely simple vagina=woman penis=man classification
There's a spectrum of opinion which is easier to consider with hair color identity as opposed to gender identity
If there's blonds & brunettes, the existence of redheads doesn't mean blond vs brunette is moot. & don't even get started on dirty blonds. But if a blond dies their hair brunette, are they blond or brunette? Their roots still say blond. But they put much care into dying frequently enough that the roots aren't visible. So society accepts them as brunette. Meanwhile the more pro-identity group will argue that not only is the blond brunette, but has _always been_ brunette[1]
The latter argument is much harder to defend, & from what I can tell arguments tend to do one of two things:
1. both parties focus on arguing against the weakest arguments of their opposition, leading to two parties talking past each other
2. both parties shift the argument to the most debatable point either way, which can often shift the dividing line of for/against to be at some extreme as opposed to in the generally accepted gray area between the extreme & the counter
Full disclosure: I'm fine using people's preferred pronouns even if I believe in biological gender (ie I don't believe pronouns need to be tied to biological gender, because while I generally need pronouns for everyone I may refer to, I generally don't care about their genitals). That said, I mostly find gender roles a hassle; being a man who has enjoyed wearing a dress & putting on nail polish doesn't mean I identify as a woman
[1] out of politeness one may not want to make a point of randomly pointing out that a brunette haired person was actually born blond, even if they don't believe they were always brunette
Despite the messiness of biology it is, has always been, and always will be a reasonable statement to say that "boys have a penis and girls have a vagina". That really shouldn't need saying. Of course, the meaning of the statement depends on the meaning you assign to "boy", "girl", as well as "penis" and "vagina". But in the semantic/communication environment in which we operate, the statement is reasonable because most people define those words such that the statement evaluates to usually-true. And usually-true is what we work with in biology and language; it's not computer science, it's messy, so approximate language is appropriate.
Your lack of medical knowledge is just as stunning.
Not only does intersex exist (yes, humans can indeed have both primary sexual organs, though it's rare), there's also a plethora of conditions that blur the line, from De la Chapelle-Syndrom to Swyer-Syndrom. There's chromosomal-, gonadal-, hormonal-, and anatomical variations that are part of "basic human biology" yet result in individuals that cannot easily be classified by vagina=woman and penis=man.
Shocking, I know.