I often see a form of argument that goes: a policy is not perfect, therefore anything that is not that policy is preferable.

You see this in complaints about the war: the execution of the war is not perfect, so it was a mistake to have pursued it at all.

It seems to me that the complaint against freedom mentioned here is similar: market capitalism is not perfect, so whatever I recommend to replace it must be better.

Yes, the market is not perfect: many of its strongest supporters can only muster two cheers for capitalism. But nothing is perfect, and pointing out imperfections is less compelling an argument than some of its practitioners seem to believe.