Fear

From an interview with Brad Pitt, this is the part that struck me:

What are you so afraid of? That’s my question. Gay people getting married? What is so scary about that? It’s complicated. You grow up in a religion like that and you try to pray the gay away. I feel sadness for people like that. This is where people start short-circuiting—instead of being brave and questioning their beliefs, they are afraid and feel that they have to defend them.

That's it, the key question: What are you afraid of? Because you're afraid, that much is obvious.