We need to think of this differently. In a two-party system, there's nowhere to go except A or B. It encourages binary thinking. Democrats think all good people are democrats and therefore all 'red' people are despicable. Similarly, republican-leaning people can come to think of democrats as a disease that will kill the American Dream with socialism, kill the rich, kill the babies, etc etc. They are not lunatic thinking, they're simply echoing a sentiment they've heard or read. Binary thinking and a two-party system leaves little room for grey. Add to this the squabbling between liberals and moderate democrats, and the blue tent can look unattractive to undecided voters. They just need to believe one more piece of opinion from the red people and off they go. Doesn't make them evil or stupid. Democrats need to work on looking more appealing to swing voters.