One of the great knocks on Milton Friedman was that his ideas were "out of the 18th century (due to their association with Adam Smith and Thomas Jefferson)," and were too naive for the complex modern world. Let's ignore, for a second, the fatuous proposition that support for individual rights and freedom can ever be considered "naive" and consider only the so called impracticality of a minimalist government.
During the 19th century there were two great scientific theories that conclusively demonstrated that it was possible for complex and efficient systems to arise without intelligent oversight. Darwin's theory of evolution by natural selection powerfully showed this for the most complicated natural systems in the universe; mammalian organisms. Adam Smith's invisible hand did likewise for human economic systems. In the Wealth of Nations, he proved that prosperity did not depend on government management, but rather on the unstoppable desire for individual men and women to do better by themselves and their family. In fact a strong government often damaged the economy, as it separated the self-interested intentions of individuals from economic decision making, thereby reducing efficiency.
Now, certainly, one cannot prove that some ingenious individual or group of individuals (government) will never be able to design a better economic system at a particular point in time. After all, individuals and companies prove every day that it is possible for the tiniest David to fell the mightiest Goliath. If there is anything to be said about our species it should be to expect the unthinkable. However, the question should not be whether or not it is possible for government to design a superior system, but rather is it likely and sustainable.. and what are the costs imposed on various parties.
Given that in any liberal Democracy there are thousands of ideas floating around on how to fix various problems, and that there is little scientific consensus on which policies would be better for society as a whole, it seems highly unlikely that the particular group of people with the particular set of policies that Might effect a superior system at a particular point in time would simultaneously hold governmental power to enact them. Second, while this theoretical system might be superior to a free market at the current point in time, there is no guarantee that it will be better in the long run. In fact, this seems unlikely given that technological and social change occur at such a dramatic place in the modern world.
In a Friedmanite/Smithian/Jeffersonian Free Market, however, the best set of economic designers need not be involved in government at the right time. The would instead be involved in starting various companies, inventing various new devices and generally improving society independent of authority. When their ideas become outdated, there will be automatically be a new set of ideas waiting in the wings to advance the greater interest of society. The ideas that fail will not be promoted, and the ideas that succeed necessarily bring some benefit to society (or they would not succeed). The Free Market deals with economic complexity much like Natural Selection deals with biological complexity. While it's solutions are not always perfect, the end result is usually a highly efficient system. If one were to knock these ideas as antiquated, then I, for one, would be more than proud to accept the label myself.
