There's people who are prone to react to new ideas with curiosity and people who are prone to react to new ideas with suspicion, fear, intolerance. It's that simple. You're right, it's not rational. Identity by gender/sexuality/race/etc. is so fundamental, so the latter group reacts most strongly and negatively to new ideas about identity. Religion fans the flames. Most don't take back control from their religious upbrining the way you did.