I understand how people could be not aware of this (most children's books don't cover the subject after all) and I can understand why it might make some people uncomfortable (although it does not make me uncomfortable, unfamilar things of can make people uncomfortable. I get that.)

What I, for the life of me, cannot understand is why someone, after being informed of it, would reject the notion entirely. Where does that come from? How does someone ascribe so much importance to the concept of a gender/sex binary? Just imagine if people reacted the same to the concept of political ideologies neither republican nor democrat... I cannot fathom it, nor any reason for it.