"Women are the only part of the human species capable of bearing children"
versus defining them by that role:
"Women are childbearers"
... where the latter construction has a strong connotation that that's all or even primarily what they are. I think that's problematic.
I'm not sure, but I think GP might have perceived that in the writing they're referring to.
From TFA: "Women bear children; men do not". There is no other mention of this gender difference.
Why on earth would you bring up "Women are childbearers" and this interpretation of "defining them by that role"?