Blame your worst political impulses on the anterior cingulate cortex of your brain, to be more precise.
Research being published today in the journal Nature Neuroscience claims to have found substantially different brain functions in college students who are very conservative vs. college students who are very liberal. "Nature or nurture," anyone? This is evidence that our political leanings are all about brain chemistry, not who we hang out with.
The thumbnail conclusion: liberal brains tolerate ambiguity and conflict better than conservative brains. Ambiguity equals doubt. Some brains can't tolerate anything less than absolute certainty.
The text of the research is available on-line by subscription only, though you can read the abstract. The Los Angeles press report about the experiment is available in many newspapers today.