It turns out politics not only makes us stupid. It also makes us callous.
He cites a study showing that we are less likely to project our own feelings on those with whom we have political disagreements. It's actually hard to summarize, so read the whole post.
I am definitely not a fan of partisanship after reading Jonathan Haidt's The Righteous Mind. In Kansas City, I said that when one side calls intellectual fouls on the other side, this has a value of zero at most. The problems with calling the other side's fouls, as opposed to your side's fouls:
--you may be misjudging. Often, one makes the most uncharitable interpretation possible of what the person on the other side really meant.
--even if you are calling that foul correctly, the other side may be correct over all, and you are blinding yourself to that
--even if you are completely right, the net effect of pointing out the foul may be to make the other side angrier; rather than conceding, they will look for fouls they can call on you.
If your goal is to accumulate a fan base and fire them up, then of course calling intellectual fouls on the other side is the way to go. However, I claim that if your goal is to contribute to a discussion in which fair-minded people will consider changing their minds, then calling the other side's intellectual fouls does not get you very far.
I should emphasize that I have come to this view only recently, after reading Haidt's book.