Gender is a social construct, it is dictated by societal norms. Because gender changes from generation to culture, with some generations saying that women can't wear pants, and the next saying they can, it's clear that there's no real ground for anything being specifically male or female. If something is based on such weak grounds then it can't be considered an objective basis for categorizing people, and many of the norms that are enforced by binary gender are in fact harmful to people. The idea that men can't express themselves how they want if they're more feminine in a lot of places, parents being afraid that their children will be gay because of negative stereotypes and lies about trans people; these are all ways that gender oppresses people, along with every issue of gendered oppression throughout history. I agree with Mary Wolstonecraft, that gendered oppression comes from looking at men and women as separate things, when really that notion is based on nothing concrete, it's not scientific, it's been around even before the days of Christianity. It's just as much of a stupid cult of an idea as Christianity too, because gender is a totally unscientific myth. In fact, modern scientists are rejecting the idea of binary gender as well. Read some Harvard articles on what trans identity means.
