Just filled in the GRA consultation and it got me thinking... Trans people face uncertainty every time they need to use single-sex faculties like toilets and changing rooms, right? 'What if I'm challenged? What do I say?' But no one is going to carry their birth certificate around with them. And even if they do, and they have had it changed to match their acquired gender, once they've been challenged, it's too late - they already feel shite and have had to justify their existence.
Presumably if they have the privilege of passing, this stuff happens less. Fewer challenges, less time feeling like shite. So the people who have most to gain from the GRA are the people who already have least trouble - people who pass in their prefered gender but just want a little extra confidence. (People who don't pass will still spend their time being challenged, not having their birth certificate and feeling shite. No GRC is going to make a 6'4" transwoman with a visible Adam's apple blend in.)
And predatory imposters who want to gain access to women's spaces. They'll gain too, of course.