“Monkeys and tigers, they might be male and female, but they aren’t men and women.”
Not really true, because monkeys and tigers still fill sex roles. A tigress raises the cubs. You won’t see a male tiger romping around with the kids. Male bower birds collect items to attract females, female bower birds do not do the same.
I think the issue is that a lot of people (feminists) believe that the genders have to be black and white. An effeminate male is still male and a tomboy is still a girl. Gender identity is a spectrum between male and female. Feminists and Tumblrinas have this black and white world view, so any deviation of the perceived male/female now needs its own category.
It’s all downhill from here.