Then in your logic, people are mentally ill for believing in God.
If people can believe texts written in old books, then people are aloud to believe in Tumblr posts.
Believing in more than two genders is just a belief. Not everyone feels all the way male or female. And too some people, identifying as something else is a fair solution.
And why dragging people who believe in more than two genders into this, anyway? What does it have to do with trans people?
There is nothing wrong with not feeling comfortable with the gender you were born with. It's not hurting anyone. It's completely harmless, believe it or not.
You people act like they can't make up their minds on what gender they feel comfortable being. That is lie. A majority of them do make up their minds.
You're the one who needs help. Not me.