Simple practical questions here, OP, no philosophical pondering required:
Do people born with female reproductive systems face (during childhood or adulthood) any forms of violence, discrimination, harmful/limiting stereotyping, or marginalisation, on the basis of belonging to the class of people who are born with a female reproductive system? Do they suffer any forms of oppression which are uniquely or disproportionately experienced by them?
If so, should there be a word to describe that group, one that distinguishes them from the dominant group (i.e. those born with a male reproductive system), so that they can be recognised in law as a group that's been disadvantaged, so that they can organise against their oppression, create safe spaces for their group, and keep track of their progress (political representation, pay gap stats, etc) and their continued vulnerability (male violence stats, etc)?
If a new orthodoxy emerges which means that there now is no word specifically to describe people born with a female reproductive system, that the word which used to describe them now describes - in society and in law - anyone at all who says so, and that therefore particular spaces, protections, and opportunities, all of which they fought for to redress the balance of the historical and ongoing oppression of their sex class, no longer exist specifically for them as a group, and will not exist for their daughters... Can you really, honestly, after thinking it through for a minute or two, not understand why some among that class of people might have concerns and questions about theverything new orthodoxy?
And why that concern might turn to anger when, along being told that they must accept the new orthodoxy, they are told that the redefinition of the word that used to describe them is an issue they have no stake in, there can be #nodebate, they should 'centre' the members of the dominant (male) class who wish to be described as women, but they themselves may not use the word 'women' or make any reference to their female reproductive biology when fighting for their right to contol their own female reproductive systems, or to end the mutilation of girls, or push back on the stigma, exclusion and expense that people like them are subjected to because they menstruate.
Also, even if they are lifelong feminists who have fought against the backward, misogynist idea that women should think, dress, and behave in a certain way because that's what it means to be a woman, they now must accept being described as 'cis', to signify that because they don't describe themselves as trans or nonbinary, they accept that what makes them a woman is nothing to do with their female reproductive biology, but their innate identification and comfort with the gender roles and expectations placed on women in their culture.
Oh, and if they are the slightest bit uncomfortable with any of these demands, they are hateful bigots who should die in a fire.
Come on, don't pretend you can't see sense when it's spelled out for you. This isn't about anyone being against 'trans rights'. This is about whether women have a right to express a view when the word that was used - including in safeguarding and equality legislation -to describe them (all of them, and only them), is redefined and used in such a way that it inhibits and obstructs progress toward a just society for women. Do you really think so little of women that you think they don't have any right to a view on that?