Zoe Williams is living in a very small bubble.
I went to a women only self defence class in our village hall a couple of years ago - you can definitely see the logic for that.
British Fencing has been co-promoting a very interesting project for a few years now, called "Muslim Girls Fence" (which actually covers a wider remit than fencing) - which is explicitly focused on women and girls, for obvious reasons.
By contrast, a fencing club relatively local to me promoted a "women only" taster session on International Women's Day open to "anyone who identifies as a woman".