Well quite. They say that mixed wards are more manageable than men's wards. (Though I've also heard people describe women's wards as eventful — but that might be 1. a sexist assumption that women together are all drama all the time, or 2. to do with psychiatric characteristics of women who tend to be placed in single-sex rather than mixed wards e.g. those placed in specialist PD wards.)
What I'm trying to say is that while it's great and important to try and hold back the tide of "gender"-based division, both for the wards themselves and to uphold the wider principle, the actual environment in "single sex accommodation" wards is such that I doubt a lot of people would even notice if a man happened to be accommodated in one of the rooms allocated to female patients or vice versa. In fact, it happened last time I was in (because of a sex imbalance in admissions I guess), and made no real difference except we saw him having to traipse across the ward to the gents' showers in his boxers and carrying his towel.
While, if I'm being purely rational, I'm on board theoretically and even practically with a fightback against gender-based division on psych wards, the fact is that if I have to go into a psychiatric ward again in the near future I will be vulnerable and feel vulnerable because I have no private space, I mostly can't leave, men are almost everywhere, staff supervision is minimal, we're all unwell on top of that, and there are few ways for me to protect myself from risk.
I may be put in uncomfortable and undignified circumstances with men who are grossly disinhibited, very confused, or may misunderstand my relationship to them (e.g. from personal experience, which is far milder than some other people's experiences I've heard: thinking they can act like my close friend and trying to give me expensive gifts while acting terrifyingly aggressively to others; displaying their genitals to me; persuading the 16yo me into taking drugs; squaring up to me; and so on). I'll also be around men who have a great deal of institutional, epistemic and physical power over me that I have to trust they will not abuse. (Almost all the men I've met in psych hospitals, both patients and staff, have been perfectly nice, normal blokes, obviously — but they're no less dangerous than men typically are, and some are dealing with difficult challenges that can make situations feel more volatile.)
I may also myself be disinhibited and act in ways I normally wouldn't — sex, for example. As it happens I'm attracted almost exclusively to women, but it's common for women (and men, obviously) who are manic to be open to having lots of sex they wouldn't normally have, and things could very easily go very wrong in a mixed ward in a way that's less likely on single-sex wards.
So… this is a very different environment to places like the previously strictly single-sex environments of women's shelters and women's prisons. If I had to prioritise action solely for psychiatric wards, then I personally would want to prioritise separating men's and women's wards over every other sex- or gender-related issue, including questions over where the occasional trans person might be placed. However, I can't only think about psychiatric wards; I have to think about the broader picture, where fighting back on "single sex accommodation" in psych wards is one part of a bigger battle, and can't be ignored.
Does that make any more sense?