Imagine a white person who "feels black". They start treating their hair and wearing blackface. They might even have plastic surgery to change their appearance. Next, they start listing their ethnicity as "black". They insist that they are black and have exactly the same experience as "natal" black people. Anyone who suggests that they might have different experiences because they grew up a white person (with all the inherent privileges) is accused of bigotry and denying their lived experience. They demand to be allowed to join organisations for BAME people. They insist they be allowed to apply for positions reserved for BAME people, and are successful at the expense of "natal" BAME people.
There would be outrage, wouldn't there? In fact, it would be considered racist, and rightly so.
Now substitute "man" for "white" and "woman" for "black". Why is that not considered sexist???
Disclaimer: this is my first time posting this kind of thing and I apologise if I have broken any talk guidelines. I apologise sincerely if I have caused offense to any BAME people. For full disclosure: I am a white woman.