The "Somalia" argument is a sore spot for libertarians. They either fall back on the old line of race and religious prejudice I outlined, or they claim that it isn't true Libertarianism, you see: it's anarchy. True Libertarians believe in just enough government to protect private property and personal safety; without those protections, they argue, anarchy ensues.
The only problem for libertarians is that they cannot point to even a single current or historical example of a government that functions as they imagine it should. They have no concrete, real world examples, so they ply their arguments in a theoretical construct.
Each and every example of places with little centralized government is dismissed by libertarians as an anarchistic situation, not a "true" Libertarianism. It's the "no true Scotman" fallacy, Ron Paul edition. The hellish situation in Afghanistan is blamed on 30 years of war and tribal anarchy, rather than the lack of a central government. The case of Somalia is blamed again on war, on American intervention, and again on tribal anarchy. Historical examples of feudalism arising in the absence of a centralized state, or the repeated Dark Ages that arise after civilization collapses, are dismissed as either irrelevant to the modern world or invalid because of war and anarchy. The fact that corruption and the Mafia are more prevalent in southern Italy where tax collection and central government are weaker than in the North, is again dismissed as a cultural or anarchistic issue. It's always the same argument.
Libertarianism, in other words, is infallible. Wherever it fails, it does so because the people weren't ready for it, or there was too much violence to allow it to work, or because the government wasn't powerful enough to protect people from harm.
Libertarians fail to realize that there has never been--and never will be--a government that functions according to their principles because it runs entirely contrary to human nature.