By saying "you can't be a woman if you're born without a vagina, and if you're born with a vagina you must be a woman" you're making reproductive organs the defining and most important characteristic of being a woman. This attitude was used to oppress women for centuries. We were baby makers only, and hormonal and chromosomal differences were used to say that we were too "emotional " for public life, education and jobs. Only over the last 100 or so years have our minds and emotions been rightfully recognised as just as important as our vaginas. GC is now going back to seeing our sex organs as our most important identifier and as a feminist and a young woman this really scares me. It is playing right into the traditional patriarchy, is sexist, regressive and oppressive. The fact its being done in the name of 'feminism ' terrifies me. The recent historic implications of insisting women are defined by their bodies scares me. These views are still held by conservative (often religion based) communities and we've all seen how easy it is for these groups to gain power - feminists shouldn't be helping them justify their attitudes or behaviour.
If you've seen/read the Handmaid's Tale you'll know what attitudes I'm afraid of. GCs ironically tell TRAs they are 'handmaids' when actually it is their attitude that has historically led to the oppression that Attwood (who is trans inclusive) bases her books on.
Gender is not a set of stereotypes - it's an identity based on culture, history, society , psychology and often (but not always) sex. It's far more freeing than "vagina = woman" and takes account of each of us as individuals not just bodies, which is what feminism up until now has fought for.
As an example, many trans women don't wear "girly " clothes, they identify as "masculine/butch" lesbians. Many trans men still like wearing make up and dresses e.g. in drag.
Many people would say the world shouldn't be defined as 'male / female' at all. But it always has done, that won't be changed in our lifetime. So seen as that is our social structure, it's oppressive to police how people choose to move through life under this structure based on bodies.
Thanks for reading this far and if I get one extra person to consider the harm that GC is doing, especially to young women of child bearing age, it'll be worth the condescension and vitriol that this post will inevitably receive.