From a liberal atheist, let me just say, "Amen".
We all evolved with an "us vs. them" tribal instinct. Once we've joined our tribe, there is an enormous tendency to
- try to collect and pass along bits of evidence that make the other side look bad
- ignore or downplay positive accomplishments by the other side
- be an apologist for the wrongdoings of people on our own side
- adopt 90-95% of the common viewpoints of our side as our own
And if you read this list and afterwards think, "Yeah, the
other side does that sort of thing
all the time..." then you're probably part of the problem.
IMHO, it is the single biggest problem facing the USA these days. The problem isn't liberals or conservatives, Democrats or Republicans, but tribal thinkers on both sides.