If a sexist is someone who acts in ways that negatively impact female people's needs, then I think someone who is trying to convince others that they should accept male people as 'women' based on that male person's belief can rightly be termed sexist. You might not like the term, but that is the outcome of what you are here on this thread supporting - the redefinition of the language that female people need for their progress against a millennia or more of negative sexist discrimination.
Perhaps it is the focus on 'equality activism' that is the issue. Female people require equitable solutions to achieve equality in opportunity when compared to male people. Part of that requires society to understand that female people still face negative sexist discrimination for being female from birth. That is something that no male person has ever experienced.
There is no equity for female people when male people are included in their group.
What other protected characteristic groups have been told that they need to allow the oppressor class access to their provisions? What other groups are you, an equality activist, directing who should and shouldn't be included in their characteristic?
'Biological difference has long been used to justify the oppression of women—to confine us, exclude us, and deny us autonomy. But just as we’ve resisted the idea that having a uterus should define a woman’s value or destiny, we can also affirm that womanhood is partly a political identity shaped by shared struggles within a gendered society—not solely defined by biology'.
Do you honestly think that feminists were working all those decades to erase the biological differences between the sexes? No. They weren't. When they said to society that female people should have 'equal rights', even then the feminists understand very well that this was 'equal opportunity'. Because female people cannot achieve parity being treated as if we are just like male people. But that is the outcome of what you are arguing for above.
To achieve equal opportunity, female people needed equitable solutions that were based on our biological differences. That is how it was done. Those uteruses should not shape a girl or woman's career choices, or their choices in things they pursue out of interest But they do shape the needs of that girl or woman. And acknowledging that is not reductive or biologically essentialism or whatever it is getting labelled as by people who demand that some male people be treated as if they were female based on nothing but that male person's belief about themselves.
Womanhood is partly a political identity, sure. But it is one that will always be based on the sex based struggles within a sexist society. And not one of those male people you are telling women to include in their group have the life experience that should include them in the group.
So, I ask again and I hope that you might answer: What other protected characteristic groups have been told that they need to allow the oppressor class access to their provisions? What other groups are you, an equality activist, directing who should and shouldn't be included in their characteristic?