Randy Barnett explains that Ron Paul doesn’t speak for all libertarians:
While all libertarians accept the principle of self-defense, and most accept the role of the U.S. government in defending U.S. territory, libertarian first principles of individual rights and the rule of law tell us little about what constitutes appropriate and effective self-defense after an attack. Devising a military defense strategy is a matter of judgment or prudence about which reasonable libertarians may differ greatly.
He also notes that "[a]ll libertarians...oppose military conscription on principle, considering it involuntary servitude." How would libertarians have fought World War II? Would they have relied upon the allegedly universal willingness of people to volunteer?
If libertarians are willing to fight wars only when they’re overwhelmingly popular, when the threat is so self-evident as to hit almost everyone (Harry Reid excepted, I guess) between the eyes, then I guess libertarian principle requires that we wait patiently for the next big attack. How many tens of thousands of American lives is libertarian principle worth?