I get OP absolutely.
A lot of the debate seems to cetre around safety. Not much is around how women feel, and our right to set boundaries.
Yet so many advertising images etc involve women with perfect bodies. Which surely leaves a lot of us uncomfortable with our own. Plus age, social conditioning, religious background, shyness around puberty etc. Not very long ago there used to be real drives to get girls and older women swimming, and if people were to think for more than a moment they would recognise that feeling comfortable is crucial. But they have decided not to think, or seemingly, that women do not have a right to set their own boundaries.
Our local leisure centre has an women's changing room, with lockers and just a couple of cubicles. About five years ago a couple of ladies in Burkas brought their adolescent (aged about 12-14) in with them. The boys eyes were out on stalks and it was very uncomfortable. I suggested politely to the women that they were too old, to be told that I had no right to object as the British had no morals - they watched East Enders. On the way out the receptionist gave me a shrug, as if to say her bosses would not back her if she did anything. I cancelled my membership, but am lucky enough to afford an expensive private gym. I assume others simply gave up swimming.
I would feel equally uncomfortable if a woman with a penis were in the same changing room. Op and I have every right to decide what makes us uncomfortable. And great if a disabled person complains about her using the disability changing facility. The more complaints the better. We need to avoid a set up with has women and girls withdrawing from sport rather than complaining.
This leisure centre is in the borough which had the highest child obesity rate in the country. Local schools tend not to have their own their own sports facilities, indeed some have no outdoor space at all, so there is a continual throughput of school groups, at lot with ethnic minority students from conservative backgrounds. Self ID, or a failure to enforce single-sex, will be a disaster for local residents. (Though I suspect the leisure centre operator won't mind as they make the real money from selling leisure memberships to local office workers.)