My musings below are thinking more about the holding of sacred/ritual or creative spaces.
My concerns about women-only spaces began as I studied at Sussex University during my MA. I focused on a branch of academia called Queer Theory. In brief, this grew out of both LGBT activism and feminism. Put very simply, it's aims are to question the things general society holds to be 'normal'. The focus of this questioning lens is sexuality and gender, but it is applied by theorists to all sorts of research areas (for example I recently read a paper which 'queered' a religious movement).
As I studied the world of the Queer -the sexual dissidents and outsiders in our culture - I realised two things in regard to women-only spaces. Firstly, because I am cis gendered (this means I am not trans, rather my biological sex and my gender 'match' according to the constraints of culture) I had never paid enough attention to trans women and the issues they face. Secondly, when a group assumes that there is a deep connection between women (often seen as spiritual) there is a danger that the differences between women are ignored. That might sounds like a positive thing, but that is not always the case. Ignoring differences can mean that certain minority aspects of identity become silenced in favour of a dominant 'voice' (for an example of this, see bell hook on feminism and race in 'Ain't I a woman?' 1981).
There can also often be (though not always of course) an assumption of heterosexuality between all the women in a group. This assumption contributes to the sense of neutrality in the group, where it is believed that the group is free from sexual attractions, advances etc simply because there are no men present. This can be an isolating or alienating experience for bi or gay women. A friend of mine described to me how when faced with a meditation group that split practitioners into men and women (to avoid the 'complications' of sexual dynamics) she went and sat in the aisle, alone, as she felt she fit in neither group.
In pagan groups I have also noticed certain female archetypes being used to create a sense of shared identity. Having lost a baby and spent a brief time not knowing if I would ever be able to have children (I very luckily am now blessed with a daughter), I can now see how mother archetypes could be both painful and, once again, alienating.
The physical experience of being female could hold a place of substantial common ground, but once again I see more difference than similarity. Even in an experience like menstruation (and not all women experience this either), the variations of sensation and attitudes towards the process vary so much, that they might as well be describing utterly different events. Which they sort of are.
So, I think my question is this: what is it that makes a group of women a sensical group? Is it having been socially conditioned as female? (Again, this experience will be VERY different depending on race, class, where in the world you live, sexuality, personality, family-history etc and excludes trans women which I don't agree with). What is the common thread which binds women? Or which binds men? Is there one at all?
Are women-only spaces there to facilitate women to feel empowered to speak out, unhindered by listening men? If so, wouldn't it be better to all meet together and start exploring an escape to culturally created bullshit which we find inhibiting, which we're over, done with?
I wonder sometimes if the only thing we have in common with our fellow humans is just that - we are humans. We have everything, and nothing, in common.