This is a brave piece on a politically unpopular stance.
Like you, I don’t understand why the push for transgender people to be treated with inclusion, dignity, and respect is getting intertwined with a need to redefine biology.
Your position that the reproductive cells one produces (or would produce, or did produce) is the determinant for one’s sex classification makes all kinds of sense. They are reproductive distinctions.
They aren’t social or moral judgements.