Oh, I miss Barracker.
The argument that women (of any colour, religion, age) are a subset of women is not offensive in and of itself, used for proper purpose.
Entirely correct. And subset as a term has been used since forever without offence.
So long as the parent group 'women' has clear criteria, all indisputable members of that parent group may be subdivided into subgroups if that subdivision serves a useful purpose.
What is offensive is the TRA argument that black women (they always choose black) are a subgroup of women whose membership of the group "woman" is in as much doubt, as disputable as men's membership.
And that's why it's offensive. Not because of the term itself, but the way it's being utilised by transactivists.
Which is why the intent to offend is obvious when it's a transactivist speaking.
A doctor trying to statistically analyse the effect of smear tests using the word subset to refer to women who have them, is not trying to be offensive.