How are libertarians different from social democrats?

Returning to last week, Ezra Klein (the real one) wrote:

Tyler Cowen is a libertarian economist with a wildly different set of
assumptions about human behavior, the policy process, and political
change [than I, Ezra, have].

I was surprised to read this.  Let’s imagine that we asked a very smart person, but one who disagreed politically with both Ezra and me, to pinpoint how Ezra and I differ.  I believe that person would see the two of us as having very different blind spots, in both moral and positive terms, but not holding fundamentally different assumptions about human behavior.  If Ezra and I chatted about which are the most insightful movies, whether the Washington Wizards should trade Gilbert Arenas, or the best way to get magazine contributors to deliver their essays on time, I don’t know how much we would agree.  (I almost always agree with Matt Yglesias about TV shows and movies, it turns out, although I don’t love The Wire as he does.)  But I’d be surprised if we disagreed any more than I would with the average libertarian, or than he would with the average social democrat.

Of course there is a lesson here, namely that our political views don’t stem from our positive views about human nature as much as we might like to think.