@Samphiredragonfly
A "perfect TW" genuinely passing with a GRC who can use the ladies and behave perfectly normally will theoretically, it's fair to say, not cause any stress or fear to the women sharing the facilities or be remotely intimidating. I do not deny that any such people exist, theoretically as I wouldn't notice them you could argue that there's a confirmation bias to thinking no TW pass properly as the ones you notice didn't. OTOH I've seen persuasive evidence that men and women seem to look for /at different stuff when deciding the sex of a stranger and seen plenty of TW whose sex was perfectly and immediately evident to me who were totally confident that were the most gorgeous and should and did definitely pass for sure. And that's the crux of the problem, a man who has gone to significant time effort and expense to hide the fact that he's a man and believes he has been successful is likely to feel rather upset, embarrassed, even offended by being told he didn't do as good of a job as his (mostly male) friends told him he did.
If the problem is men in women's toilets are intimidating and uncomfortable for women. You can't possibly write a policy or law that actually differentiates based on how effectively a man is hiding the fact that he's a man. That can vary from day to day and even from minute to minute. Any rule which says that women are responsible for judging the appearance of TW and effectively telling them that they aren't pretty enough / good enough so they shouldn't be here is a terrible idea because that's a shitty and unreasonable place to draw the line. It is shitty for the TW and does absolutely nothing to 'fix' the problem of women's dignity privacy and needing to feel safe and comfortable. You can't be here because you didn't do your hair properly today and I can tell that you're a man, but you are entitled to be here when you're having a good hair day is not a solution.
So there is no way to keep out the 'will upset and intimidate women' TW without also saying the 'will pass actually' TW should also not be there as TW it turns out are actually sometimes really rubbish at telling whether they are passing or if women are just being too polite to say that they aren't. And that's even before you get into the requirements of certain religious groups where women need to be able to access a single sex space to participate in society. Or the fact that certain TW seem to really want to intimidate and upset women.
Clarity that its ok to say this particular group / changing room / toilet area is single sex sends a clear message of who is entitled to be there. Therefore if someone is there who is not entitled to be there is you can reasonably ask them to leave. Women can then expect back-up from police / management, should they need it, to enforce a clear and consistent rule. This loo is not for TW is a much fairer and more sensible rule than this loo is not for TW who aren't pretty enough.
Shoplifting is illegal but it does still happen, stopping people from shoplifting is not necessarily easy. As a shopkeeper of course you don't notice every time someone shoplifts but it does mean if you catch someone you can bar them and/or call the police. And if you see them again you can tell them to bugger off.
Which is where we come back to third spaces; I mean let's be clear TW can use the men's - assaulting someone is already against the law, should a man assault a TW in the changing rooms or loos he is in the wrong and should frankly be prosecuted. TW should be able to rely on the police or management to support them if such an incident occurred. But given how vocally supportive so many men are of TW it feels like men aren't so hostile as we're being asked to believe.
I think when GRC were first introduced women assumed the gatekeeping would be better, that in order to get a GRC men would be in that 'perfect' category by behaviour if not always completely by appearance. That someone would be in effect performing checks and balances that considered women's dignity and privacy before issuing the GRC. That the TW would be those we wouldn't notice. That hasn't worked and it clearly isn't what Trans people are saying they want.
You can have non binary identities or even 57 genders, gender fluidity, no gatekeeping culture - but then you can't have your sex based rights changing day by day. and this is where the wise women of mumsnet have been for some time; It becomes a question of do all men or none have the right to walk into the women's loos, women's changing rooms, etc. Basically sex based categories have to remain sex based as gender identity is too fluid personal and nebulous to be of use where sex matters.
Anyone, regardless of their feelings on gender identity; if they would claim one or which one they would claim, can resist sexist bullshit where sex doesn't matter.