Also, talking about undisputable biological facts, it is an undisputable biological fact that a lot more can go wrong in the development of male external genitals than in the development of female external genitals. Not least because male genitals develop from something very much akin to female genitals during embryonal development. It is therefore an undisputed fact that most intersex babies are genetically male.
It is also an undisputed fact that a surgical intervention that subtracts is easier to perform than one that adds. It's for this reason that a lot of genetically male and phenotypically intersex babies are assigned female, and often have major parts of their genitals removed in "corrective" surgery very early in their lives. If a (genetically male) baby is born with a split scrotum and an underdeveloped penis, common practice is, or was until recently, to take away most of the visible part of the penis so that it would pass for a normal clitoris soon after birth. Yes, it's as cruel as it sounds.
Anyone deserving the label "men's rights activist" should be up in arms about this cruel treatment of some genetically male babies at the hands of society believing in the delusion of binary sex so strongly that it considers anything departing from it as needing surgical intervention. I can get pretty enraged about that, and I don't call myself that.
But Metaphor is not only silent about the fate of intersex children, he handwaves it away when others bring it up. This shows that his crusade isn't about actual injustices, but about people who have the audaciousness to question a naive-biological binary view of sex.
ETA: In other words, we live in a world where male babies routinely have, or had, most of their genitals removed with society's blessing and without the ability to consent, but that's not what he wants to talk about. Instead, he chooses to point fingers at consenting adults.