Sexism is the belief that one sex or gender is superior to the other. It can also mean that one sex or gender is archetype of the other, that is, that one sex is based on and understood in light of the other sex.
Trans 101: Pro-Binary - You don't have to be sexist to be pro-binary, but it comes very easily
Objection: True Masculinity/Femininity
Trans & Gender 101 >