Here’s my two cents. It’s hard for people to keep up with the euphemism treadmill. There was a time when the word “female” didn’t have the negative connotation that it does now mostly thanks to co-opting by incels. It should also be stated that the word “male” doesn’t have the same negative connotations and it’s similar to how there’s slurs for black people but none for white people.
So why do people find “female” offensive? Well for starters it’s dehumanizing. Women is a less academic term and female implies some biological essentialism. I think the crux as to why it’s a big deal now is that women do not refer to themselves as females in the manner that men do. Men do not think of themselves as males, they do not call other men males, men call themselves men. male and female are simply outdated terms.
I suspect one day as society moves towards a more genderqueer position men and women will become unacceptable to say too. Idk. Like I think we need to acknowledge that there is such thing as a euphemism treadmill, that languages change, words become offensive or nonoffensive over time, and like all we can do in order to be a fucking decent human bean is to conform to society’s standards as to what is acceptable as according to the treadmill. Unless it’s some shit like calling the homeless, the unhoused. Then in those specific instances we got to run against the treadmill. But in this specific instance, we need to run with the treadmill on this one. Nothing feels better than conforming with society.
Interestingly, my partner and other friends who are women and whose first language is not english usually use 'female'. It usually rubs me a weird way, since the only other people I interact with who use the word aren't the most respectful towards women.
In my mother tongue, the word for women implies subservience, my mom told me not to use that term when referring to women close to me, instead to use another term which is for endearment (cousins, good friends, etc) or yet another to refer to them respectfully.