Gerson (columnist) makes a good point in his essay here: "We know that many of our attitudes and beliefs are the brain's justification for pre-rational tendencies and desires." Politically encamped left or right, a lot of us substitute feelings for reason at times, a bit like a long-running family dinner fight, opponents retreating to their respective Facebook corners afterwards. 

We then go out and vote, hoping that THIS time, winning will settle that fight. It doesn't as it can't.