Why does blind faith in a political affiliation over-rule rationality and common sense?

I think people are innately tribalistic and the best way to separate yourself from the other is to pretend that they are inherently different from you.

So liberals are evil commies and conservatives are evil rednecks and everybody gets to feel like they're the good guys without having to accept the fact that we're all just people most of whom are working to the good. We just happen to have different ideas of how to get there.