Krugman dismisses libertarianism because of the foil of imperfect politicians. This coming from someone who has spent the last year crying in his column that corrupt politicians wrecked the “stimulus package.”
Libertarians are quite cognizant of corruption of politics, having, frankly originated the the field of class analysis in both classical(Laissez faire) and neoclassical economics(Public Choice). This is why radical libertarians advocate for a de-politicized social and economic system(anarchy). Otherwise, I certainly agree that contractual tort restitution can be spoiled and rendered inefficient by actions of the political class. However, it’s not like Krugman’s preferred political arrangement, “social democracy,” doesn’t suffer from the same public choice faults. Indeed, in Krugman’s ideal arrangement, everything is decided by politics, which makes the public choice problem paramount. Krugman’s solution to the problem, especially since he has turned into a political hack, seems more or less two-fold (1) politics as means of de-legitimatizing dissenting views(the effective one party State) (2) crises as a means to impose his preferred institutional paradigm(“Disaster Corporatism”).
You can label radical libertarianism as not being a serious option, but Krugman’s alternative is tyranny, that is, unless you happen to agree with Krugman.