Well, that journey is mine. I'm not a gay man, clearly, but I have supported trans rights for 15 odd years. Saw it as akin to supporting gay rights. I knew a transman at college and so to me, it was all about ensuring, as Stonewall put it, 'acceptance without exception'.
My conversion was equally rapid. Lots of ignored cognitively dissonent moments, then researching to prove all of you wrong, which included Pink News (and if that doesn't get any sane women scaling mountains in short order, nothing will).
The thing is, as he says, what used to be about ensuring freedom from and freedom to for a small group of badly marginalised people has managed to slide into full blown Men's Rights Activism.
I still support legitimate trans rights. I just don't accept that women have none, and nor do I accept that what the penis-possessor wants, the penis-possessor must have. Which, when you cut through the bullshit, is pretty much what modern TRAs demand.
I also hope that the friend has made it clear to HR that he withdraws his complaint, and accepts the PP's right, as a woman, to hold views on issues affecting women's rights.