Why are liberals so condescending?

I present for you a Washington Post piece in which Gerard Alexander attempts to answer a question I have long pondered.

"Every political community includes some members who insist that their side has all the answers and that their adversaries are idiots. But American liberals, to a degree far surpassing conservatives, appear committed to the proposition that their views are correct, self-evident, and based on fact and reason, while conservative positions are not just wrong but illegitimate, ideological and unworthy of serious consideration. Indeed, all the appeals to bipartisanship notwithstanding, President Obama and other leading liberal voices have joined in a chorus of intellectual condescension."

Read the entire article.