Like many here, I started out where you are OP.
I am a life long left wing voter, and always thought of myself as liberal and 'progressive'. I cried when I watched 'Boys don't cry' in the cinema, and wished people would be more accepting.
SInce I understood what TRA's are asking for, I have totally come out of the 'grey'. There is no grey area or compromise between 'Transwomen are women for ALL purposes' and 'no they're not'.
When I was first having my awareness raised, I saw toilets as the greyest area.
We're all in separate cubicles with doors, so what difference can it make if a man, who is so distressed about his sex that he has had genital surgery and medical treatment to look more like a woman, is in there as well? He only needs to pee, right?
Then I read more about how some women, less fortunate than myself, feel about being vulnerable in the presence of a strange male. Women who have been victims of male violence may have such a strong fear response to strange males that they are unable to use mixed sex toilets. If there are no female only toilets available for them they may have to exclude themselves from full participation in society.
I have read the sexual fantasies of autogynephiles on Reddit, about the sexual thrill they get when using women's toilets, and even how they search through sanitary bins for used tampons. I have seen the videos men have posted on Twitter, filming themselves masturbating in the presence of unsuspecting women. Women should not be used as props in men's sexual fetishes.
As a teenage girl, I was 'flashed' by men several times. Every woman I have ever asked has experienced this. We know that 'flashing' can escalate to more serious crimes. If a man is accused of flashing in a park, at least he can't argue that he had a legitimate reason for his penis being exposed. This is a lot of more difficult in a toilet - he may have 'accidentally left the door ajar'. Why would we make it easier for these men to get their sexual thrills?
The problem isn't that all trans identifying males want to use women's toilets for nefarious purposes - I'm sure the vast majority of them really do just want to pee. But if you allow ANY males in, you let them ALL in. There is no way of distinguishing a male with severe gender dysphoria who has had genital surgery from a chancer in a skirt. They all look the same.
We have to say NO to all of them.