I found this at the Other McCain today. It comes originally from Shannon at Chicago Boyz.

The left doesn't actually have a developed system of thought regarding the economy. They can't actually explain why the real world political process will systematically make better decisions than the free-market. Instead, they simply point to any reversals in the real economy, regardless of cause, and then assert that in their imaginations, leftist politicians could have done better.

It's hard to argue against people's imaginations. You end up with a discussion much like two D&D geeks arguing over whether a dwarf with a +10 axe could take an elf with a vorpal sword.