David Friedman's The Machinery of Freedom is one of my favorite all-time books making the case for freedom. I like it on at least four grounds: (1) it's tightly written, which reflects David's tight thinking, (2) it shows a great sense of humor, (3) it's got good numeracy, and (4) in it, David is just as critical of his own positions as he is of those of other people's, something that is rare.
In his chapter, "National Defense: The Hard Problem," he especially puts (4) above on display. David is an anarchist and he uses this chapter to argue against . . . anarchism. He points out that advocates of anarchism, himself included, don't yet have a good solution to the problem of national defense.
These arguments suggest that it may be possible to defend against foreign nations by voluntary means. They do not prove that it will be; I am only balancing one imperfect system against another and trying to guess which will work better. What if the balance goes the other way? What will I do if, when all other functions of our government have been abolished, I conclude that there is no effective way to defend against aggressive foreign governments save by national defense financed by taxes--financed, in other words, by money taken by force from the taxpayers?
In such a situation I would not try to abolish that last vestige of government. I do not like paying taxes, but I would rather pay them to Washington than to Moscow--the rates are lower.
When David wrote that in 1973 and revised it in 1989, his last statement was true. Implicit taxation in the Soviet Union, given that the government claimed ownership of almost everything, was very high. Now it's false. Russia has a flat income tax rate of 13 percent, far below the U.S. rate. What would David say now. :-)