Catching up with this thread...
Though the conversation moved on, it occurs to me that the poster flagging the difference between purpose vs function was making an insightful distinction, although not the one that was intended.
Evolution doesn't start with an end goal in mind and think up a solution to meet it. Evolution doesn't have a mind, it is just the name we give to a hugely complex multi-intersecting process of trial and error.
So while I entirely agree that this was not the sense in which "purpose" was being used when that poster seized on it as an opportunity for bad faith misrepresentation, if you consider "purpose" as synonymous with "intent", then unless you believe in a Creator/Designer it is correct to say there is no purpose behind our natural anatomy.
However fake anatomy only ever comes into being by conscious choice of a human. It does have a Creator/Designer. Therefore I would say it does have a purpose. Without a human's desire for it to exist it would not exist, and therefore that human's purpose for it is relevant.
So for that meaning of purpose, questioning the purpose of fake anatomy is a valid question in a way that questioning the purpose of natural anatomy is not.
So ironically, in trying to obscure the difference between real and fake anatomy that poster actually hit on a fundamental difference between them.
Going back then to deal with the supposed "gotcha" of women (original sex based meaning) who have medical procedures to repair or create female anatomy, the poster's argument was that any question about the purpose of fake anatomy in the male could equally apply to the female.
At which point I say "yes it could".
The critical word here being fake.
What is not valid is what that poster was doing in comparing fake pseudo "vaginas" surgically created in men to natural "blind vaginas" in women with congenital defects or post-hysterectomy. The latter was always there, only thr forner was created with intent for a purpose.
But to the valid comparison of a medical practitioner attempting to create a surgical pseudo vagina in people of either sex (noting that even taking on board that women (osbm) can need such surgery the number of female people who have no vaginal structure at all to start from and need the whole structure created feom scratch in the same way any male person would is surely incredibly small) I would entirely expect that practioner to have an informed conversation with the person in question regardless of their sex to understand their expectations and yes, purpose in having the surgery. These are not trivial interventions so the person undertaking them needs to consider whether they are worth doing.
And yes, for the small number of female people born with vaginal agnesis, undoubtably sexual function is a driver for many of those who chose medical intervention.