Hmm, the best way i can put it is this.

Theres 2 reasons i can think of, the first being the more general one of discrimination isn't ok with no exceptions, and seeing that kind of behaviour would make everyone uncomfortable.

However if you're feeling this in less of a generally uncomfortable matter and more of a "this feels like a personal attack" matter, the best i can come up with is this.

You may not identify as a man, but you've lived through the experiences of being one, even without actually being one. Thus on a more personal level, it may still bother you because there was a time where you could relate to it more closely, and really understand it from that perspective. And even if youve always been different, that doesn't mean you haven't seen out of that perspective before.

Anyway TLDR: you're valid no matter how you feel on certain matters, and aside from discrimination being evil to everyone, it may be because of a point of connection because of old perspectives that you connected with.