Sometimes being a single issue voter happens because people just care that much about that one issue. But there’s a natural tendency for anyone’s decision to come down to one thing. Complex issues are complex, most people don’t know what’s right. But then they do have ONE thing that they consider black-and-white, so that influences their choice. It gives them something they feel they can say to others “I just can’t bring myself to vote for someone who XYZ…”

Because let’s face it: no one wants to hear your entire list of political calculations. People’s choices are absolutely influenced by thoughts of how they’ll justify themselves to the people they know. And having one big pithy thing to say is more convenient than a subtle position based on a score of factors.

Humans are social, emotional, idiosyncratic shortcut machines, not logic engines.