"For example, for certain medical purposes – tests for different kinds of cancer, say – it would be most useful to divide people up based on their internal reproductive organs. "
Yes because everybody knows exactly what internal reproductive organs they have, with no reference to any outwardly visible characteristics.
So they say men can be women because some people are intersex and who is anyone to say by looking at the outside whether a person is male or female.
At the same time we all have to magically know what internal organs we have, without ever having seen them or had scans for them, and without linking them to our externally sexed bodies in any way.
It's all claptrap.
This person obviosuly supports campaigns for "people with cervixes" (and so what if a large proportion of people with cervixes don't know that they've got one and this means them).