The funny thing about high school students (and maybe all of us) is that they love to take a point of truth and generalize it to be a rule. Gay marriage can’t come up at school without the kids figuring all LGBTQ people want to be married.
I think maybe this human need to put things in boxes is part of the reason people struggle so with trans folk. People have clear expectations for lesbians and gay men. They may not like it, but to some degree they understand the nature of it and are able to apply the stereotypes necessary to make peace with it. But changing genders? Even liberals can get a little jumpy about that one.
Men are particularly funny about this topic and why I have come out to so few men. They can not imagine not wanting to be a guy! I get the feeling from many that I have voluntarily left the Yankees to play for a minor league club.