I've been skimming to catch up, trying not to disrupt wherever the thread of thought is now, but saw this and had to reply. Imdunfer, in the context of your other thoughtful posts, it really surprised me. I mean:
Person A, arguing for lowering the speed limit outside their kids' school: "I think a legal limit of 30 would safeguard our kids - stats show cars going at that speed cause significantly fewer injuries and deaths".
Person B, arguing against this: "So, exactly how are you going to stop people breaking the limit?!"
Since I'm now interrupting anyway, I'll also add what I thought when you hypothetised about the 5 foot 4 effeminate male.
Besides the obvious thin-end-of-the-wedge issue (I mean, to echo the above, "exactly how are you going to measure the height and/or femininity [of aspirant entrants to this hallowed space]?")...
...The first thing that came to mind was that parts of your description could well match the three young boys recently let off with a slap on the wrist for rape. It's certainly a fair description of a large proportion of younger teen boys, many of whom could still physically overwhelm most women.
For me, the strength differential is key. In a single-sex loo, I'm fairly evenly matched with anyone in there (please could no one go down the "But, bigger women / gym obsessives!" road - it would be about as silly in the context as answering the question above with "Stick a ruler by the door!"). In a loo in which even short, effeminate males can enter, the vast, vast majority (any?) of these - hormones or not - would be able to overpower me with a flick of their delicate wrist.
This is not equality.
I deserve the knowledge enjoyed by men in their equivalent spaces: that I am not wholly reliant on the good will of another person in there for my safety; that I am autonomous in that sense.
Women deserve autonomy in this and the linguistic sense.