I am far from confused. This is the entire theme of the series "politics is the mind-killer." Arguments are soldiers, and giving aid to enemy soldiers gives aid to the enemy position. I don't think people of any political persuasion are immune to this.
A article in the Atlantic, linked to by someone on the unofficial LW IRC channel caught my eye. Nothing all that new for LessWrong readers, but still it is good to see any mention of such biases in mainstream media.
I break here to comment that I don't see why we would expect this to be so given the reality of academia.