@Lostcat
Genuine question - have you considered that there is a difference between words and the things they label?
"Lesbian", "Gay", "Bisexual" and "Straight" are labels for sexualities.
The sexualities they label are "woman attracted exclusively to women", "men attracted exclusively to men", "someone of either sex attracted to both men and women", "someone of either sex only attracted to the opposite sex". These sexualities exist outside the labels and don't change simply because the words may change. If we suddenly decided we wanted to swap around the words "Gay" and "Straight" it would cause a lot of confusion but people wouldn't suddenly wake up and actually fancy the opposite sex to the one they fancied yesterday just because the label was changed!
To "deny the sexuality" of the men (original sex based meaning) who identify as women who are attracted to women would mean saying they are in fact not attracted to women. No one is saying that. No one is saying those men are not attracted to exactly who they say they are. No one is telling them they cannot form meaningful (or indeed meaningless!) relationships with any woman who wholeheartedly consents to it. All anyone is saying is that the name for that sexuality is not "lesbian", it is "straight".
Do you understand the difference? To deny someone's sexuality is to say they are lying or mistaken about who they find attractive. To entirely accept they are truthful about who they find attractive but simply deny that the word they wish to use to label that attraction means what they want it to mean is not at all the same thing.
Now, you may feel the label of "Lesbian" should be used to mean something different, something that means attraction to the mentality of women (whatever that is), something that includes attraction to men (original sex based meaning) if those men are, or believe they are (or say they believe they are) women (new mentality meaning). And sure, argue for that. But don't try to claim that saying no to a change in label is somehow denying a person's sexuality.
FWIW, I have no issue with there being a sexuality that means mutual and exclusive attraction between people of the mentality of women (whatever that is), I just don't think it is reasonable to say this sexuality is somehow the true meaning of the label "Lesbian" when it never was before, and when many women exist whose sexuality is exclusively attracted to women (both in the original sex based meaning), a sexuality which until very recently was called "Lesbian" without any disagreement.
Given many genderists use "Femme-" for gender identities that include some element of the gender mentality of women (whatever that is), "Femmamory" could be a good label under which to recognise this new, emergent sexuality without appropriating "Lesbian" - leaving both groups fully recognised and valid and different. Win-win!