awaitingthematriarchy answered:

Because when ‘woman’ becomes redefined to ‘anyone who wants to be’, actual females lose what sex-based protections we have. I lose the right to object to being strip-searched by an airport security officer with a penis. I lose the right to object to an intact male as a roommate in jail or in a homeless shelter. I lose the right to ask for a female therapist to talk through my rape with. If I become old or disabled, I lose the right to request a female-bodied carer to deal with my intimate care. My daughter loses the right to not be expected to undress in front of teenagers with penises at school. She loses the right to compete in fair sports competitions for scholarships or awards. We lose our collective right to have safe spaces away from males and to set our own personal bodily boundaries. And make no mistake, women didn’t get sex-segregated spaces for fun - we got them to keep us safe from rape and sexual harassment.

Similarly, the push to force lesbians to accept transwomen within our communities serves is a push towards erasing female homosexuality and making all women penis-inclusive by default (which is an extension of both rape culture and compulsory heterosexuality). Lesbians are female homosexuals - we are women exclusively attracted to members of the same sex as ourselves. Gender doesn’t come into it. Our homosexual attraction is innate and unchangeable, and scientifically proven to be so. If ‘lesbian’ no longer means ‘homosexual’, then what does it mean? If you try and force all lesbians to identify as pansexual, and shame us for our homosexuality, then you are trying to forcefully erase our existence as female homosexuals, which is an act of bigotry and homophobia.

Hope that clarifies my position.