You mean
genetically speaking, not medically. In this very limited scope, the person in question is still XY, but in terms of medicine (even in terms of biology and genetics) this means very little. As with the question of reproduction, I doubt you spend time genetically screening your partners to see what their chromosomes are, yet people who were born female can have XY chromosomes. ZOMG, you could be sleeping with a dude and not even know it!
...What? The all important chromosomes said so! So what if she has a full reproductive tract and was born and raised female. Obviously, she's a MAN!!!!!!!!!!!!!!!!!!!
The difference between male and female is actually quite tenuous. This isn't looking at something logically, it's cleaving to an excuse.
And using science to justify his views on the matter is perfectly valid.
Yes, but slapping "science" on something that's not scientific isn't. And that's why we're here right now.
Look, we've got actual biologists on here who have spoken to this exact concept in prior threads and hopefully have or will speak to it in this thread better than I possibly can. I will instead reiterate that these claims of medical intents are bogus. Please don't defend things unless you know what you're talking about.