The truth is, I don't yet know. I've been thinking about this for a long time and still haven't made up my mind about a few aspects of this complicated situation.
There is nothing remotey complicated about the situation, you and others like you are deliberatey trying to make it complicated for reasons known only to yourselves but in my opinion are rooted in misogyny and homophobia.
Everybody on this forum is certain. Dead certain. Xx Is female and Xy Is male. There is only this. There is no gender. Usage of a sexed space must rest entirely on the makeup of your blood: your chromosomes.
Spaces and some services are delineated on the basis of SEX for obvious and prefectly reasonable reasons - safeguarding being one reason - not on gender which is a concept that has more definitions than I have had hot dinners.
I find this reductive, naive and discriminatory. It forces people to use spaces designed for their sex at birth when they might have been identifying otherwise for decades. It might terribly humiliating not to mention risky, to walk into that space and be a target for bigots or macho drunk guys. But this, you say, is the price of your kind of absolutism. (The fact that it is someone else's price to pay, and not yours, is just by the by).
It is not in the least discriminatory, reductive or naive. Everybody is either one of the only two sexes there are in the human species. The law has been clarified that people of one sex should never have been using faciities and services for the other sex and nor should they ever have had any expectation of so doing. As said above those spaces are provided on the basis of sex not identity.
You don't think it is humilating or risky for women and girls to be expected/forced to undress in front of men or boys when they do not want to? You don't think women and girls have the right to consent whom they remove their clothes in front of or who they toilet alongside?
Women and girls have already paid a high price due to single sex spaces and services being in breach of the law.
Many transwomen already access the male single sex services and are happy to report absolutely zero problems doing so and there are absolutey NO reports anywhere (and believe me I have searched extensively) of transwomen being at any risk or being attacked using the services that correspond to their sex.
While I'm sure of all this, I'm not sure how it should work if somebody identifies as trans and feels trans but hadn't made any changes to their outward appearance or biology. Can it pave the way for a mass invasion of women's spaces? I doubt it but I am not as sure as you all seem to be about your position. You put all trans people together; I suspect there might be different rights of access and usage but I know I'm setting myself up for a virtual bloodbath here.
How? How would this work? The simplest solution is the solution that has always been the case that where spaces and services are required to be segregated on the basis of sex they are with no exceptions. Should trans people feel unable to access the spaces and services for their sex the onus is on them to campaign for alternative, additional provision.
Trans women competing with born-women in sport? Another thing I'm still trying to learn about so I can form a meaningful opinion. Not there yet. My daughter was regularly beaten by a trans girl when they were little: I didn't love it and interestingly, nor did the mother particularly. There's that. Unlike most on here, I am not an absolutist and I don't think this is simple.
Both you and the mother of the trans girl clearly weren't that bothered or you would have done something about it. What a lesson to teach your daughter that they are not entitled to fairness and their mother won't fight for it on her behalf, that your daughter must place herself second to the feelings and desires of the male sex. Fabulous.