There is something all women share, to be called 'women.'
It's not height (tall or short etc.) or race (black or white etc.). It's not even, say, income or occupation or eye colour, or star sign or favourite food or marital status or political affiliation or religion or weight or hatred of beetroot or love of Agatha Christie. And so on.
We are seeking for the one thing all the very diverse women share, to be seen as members of the same group. And traditionally that has been being a human being of the female sex.
The above quote argues that it's not at all necessary to be female for someone to be in the group 'women', and if we take this as a hypothesis, then we should ask what, in their framework, replaces 'being of the female sex' in the definition of 'woman'.
And here I, at least, founder, because we are told that a person is a woman if that person says so, pretty much. It doesn't really matter if the underlying justification is an abstract gender identity or the many alternative explanations I have seen offered.
Once we dispense with something that can be objectively established we have destroyed the basis for even having that category. Why would we need categories reflecting how much people love or hate the colour pink, long hair, high heels, cars, trains, being choked/choking others in bed and so on?
The erasure of sex as the determining factor in who belongs to the category 'women' matters.
It matters, because female people are still the largest oppressed group on this planet, and erasing their name and existence in languages and laws makes fighting that oppression extremely cumbersome, if not impossible.
It matters, because the two bros, sexism and misogyny have no trouble defining what a 'woman' for them is, but we are stripped of the tools to fight them because the gender identity movement prioritises 1950s rigid gender roles and sexist stereotypes about femininity. This will make things worse for most women, not better, even in countries where women's legal rights already exist, at least partially.