Here my take on it, and it’s ref transwomen not trans men.
There is small number of men with true gender dysphoria. From what I’ve seen these men tend to be younger. They will take hormones and will some surgery. Any trans woman who has bottom surgery will have my undying respect.
To be legally a woman you need to get a Gender Recognition Certificate. There were certain conditions which need to be fulfilled. Ie over 18, you have been diagnosed with gender dysphoria. You have been living as a woman for 2 years, and intend to to stay this gender for the rest of your life. You can apply even if you haven’t had any surgery or treatment, and don’t intend to.
There is another group of men who have various forms of autogynephilia. These men are aroused sexually by the thought of being a woman or dressed as a women. In the old days it was called a kink, or fetish. They were called cross dressers. I’m not sure if you could include peeping toms in this group.
There is also a third group of men who are sexual predators of young boys and girls, teenagers and women. I remember hearing a (nice) policemen saying the general pubic have no idea of the lengths these predators will go to, to have access to these mostly women and girls. They will happily dress as a woman if it means that they can go into womens spaces.
By giving the first group, the genuine gender dysphoria men, access to womens changing rooms, toilets, sports, prisons, and other single sex spaces, you are also giving access to the other two groups of men who have more sinister intentions.
The argument for TWAW (transwomen are women) is that this group has been severely discriminated against. In the same way we have legislated for equality for women, other races and people with disabilities, we should also legislate for Tw to be classed as women.
I don’t know how many of each of those three groups of men are out there. My personal opinion is that the first group of TW, do not outnumber the other two groups of men (cross dressers and predators). But I do know that the population of women is slightly over 50%.
So the very crux of the problem is, should women give up their private, safe spaces, so that a very small percentage of the population can have equality.
Women feel that we have fought long and hard for the rights we currently have. If we lose the right to single sex spaces, we are not only letting men in, but we are letting in some men who actually have bad intentions to girls and women.
If TWAW, then 50% of the population is shafted. If it’s the other way around, and you exclude the predators and fetishisists, then it’s a very small percentage of the population (1%, 5%?, I don’t know), that will continue to be discriminated against.
I hope what I’ve said makes sense.
If any of the wiser mumsnetters think I’ve got anything wrong, or my reasoning is addled, please let me know. As I said, this is just my take on it.