Via Bryan Caplan:
My point, of course, is that whether or not you agree with Arnold [Kling's] view that government is a good idea, he needs better arguments. I suggest the simplest: For reasons that remain poorly understood, the status quo in the Western democracies currently provides the highest standard of living in human history, and any radical change has a serious risk of ending in disaster.
I think that this statement presents consequentialist libertarians with a problem: why fix what isn’t broken? Can consequentialist libertarians guarantee that their proposed changes will in fact result in better consequences for the folks they’re seeking to persuade? At the very least, can they promise that their proposed changes won’t make folks worse off? The answer, of course, is that they can’t make any such promise. They can’t even provide probabilities.
In fact, the most persuasive consequentialist argument is that since Western democracies, despite their warts, have consistently produced the best living conditions in human histroy, no changes should be made whatsoever unless and until something better proves itself. To claim otherwise is to risk throwing away the most desireable consequences in all of human history.
This leaves consequentialist libertarians with very little to do except wait around for something better than Western democracies to emerge, and to argue against any changes to Western democracies in the meantime.
After all, welfare states are the best thing there ever was.