Why are liberals so condescending?

From Gerard Alexander in the Washington Post:

"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."

And here is a perfect example of that liberal condescension. They just think we are all stupid and therefore progressive ideas and policies passed down from on high are the only things that can save us poor, stupid souls.