The Burgess Shale

I don't know. I'd be very interested in seeing any studies that have been done. But it is the lived experience of many women that they are disbelieved explicitly on the basis of being female and thus having a single-sex "safe space" to discuss that in can be a very valuable thing. The blog that I linked to self-identifies as a feminist and predominantly-female space. There is certainly room for other spaces that aren't female-labeled.