An old cliche tell us that “All the music you don’t like sounds alike.”  Does the same hold in politics?  Does everyone on “the other side” sound the same?

They don’t to me.  Krugman, Rawls, Marx, and Lenin are all left-wing in some sense, but I wouldn’t say that they’re “formally committed to similar political beliefs.”  It’s puzzling to me, then, that Matt Yglesias would say exactly this about me and Tyler Cowen.  While Tyler and I are the best of friends, we constantly disagree.  (See here, here, here, and here for starters).  We certainly disagree more fundamentally than say Obama and McCain, or even Reagan and Carter – and lots of people think that their disagreements were major.

What would account for the misperception of libertarian homogeneity?

1. People generally misperceive their political opponents as more homogeneous than they really are.  On this theory, most libertarians would consider Krugman and Lenin’s political beliefs to be similar.

2. People misperceive non-mainstream political opponents as more homogeneous than they really are.  On this theory, the typical Democrat would also see Marx and Lenin’s political beliefs as similar.

3. People mistakenly equate amicable disagreement with fundamental agreement.  On this theory, non-libertarians would not lump Cato and Mises Institute people together.

4. There’s no misperception; lumping your opponents together is just a rhetorical tactic to lower their status.  On this theory, people wouldn’t equate dissimilar dead belief systems.  For example, since the Catholic-Protestant dispute is irrelevant to modern politics, we would readily acknowledge the differences between Luther and Loyola.

#2 seems closest to the truth to me.  Is it?  Got a better explanation?