The most important point, also made by Cristobal in this thread, is that for the word woman to exist at all, and for some people to identify with the term over man, there has to be a through line that objectively connects all of those under that label. Something outside of our own minds and subjective experience. I think the problem stems from some people wanting to equate the word woman with female, and others wanting to say that to be a woman is ONLY what an individual says it means for them personally and has nothing to do with their biological sex. So a person could be female, but not a woman. Male but not a man. If that's the argument, it starts making more sense, but it still begins dissolving the word woman entirely. I also think that many Trans men and women might not even admit to technically being a biological male or female which is to me to a truly deluded denial of objective reality.
I think the thing that people don't realize is that without a clear definition of the word women, it doesn't stop there. That means that lesbian, bisexual, gay, trans, etc. also all lose their meaning as all of those terms are meant to define a person's attraction to and identification with specific genders. How exactly could a person be gay because they're attracted to "the same gender" when that gender has no clear definition? What exactly makes them gay if they're a man who likes men if man has no throughline quality? I feel that the refusal to offer a simple objective definition of these words is doing more than simply attempting to "expand our understanding of gender" and is actually erasing the very identities of the same people to espouse it, as well as anyone who disagrees with them. Because after all, if anyone can be a man or woman, then no one actually IS a man or woman. People are trying to embolden their own ambiguous identity through the erasure of the solidified and are calling it progress. I call it insidious group think.