Problems

I sat down once and thought hard about where some philosophies ultimately lead.

I got some surprising answers, but I never really put them up for debate.

It occurred to me that feudalism is a logical conclusion to libertarianism.  Feudalism is all about property ownership and the rights of property owners.  Even if it's not where it will ultimately end, there's nothing inherent in it to violate a libertarian's sensibilities.  In practice, it is much less libertarian, but it's not too hard to see a functional feudal-libertarian society.

Slavery is also A-OK with libertarians; provided that the slave sold himself willingly or as a punishment for a crime.

Interestingly, the nation-state system is a good way to point out some of the flaws about getting a libertarian society going.  I'll try to find some simple examples and post them later.  Actually, what Germany was up to in 1939 is a fairly decent example.  Germany absorbed, attacked and conquered several nations with little to no interference from nations not attacked.  What does libertarianism do to solve the, "it's not in my interest at all to honor the contract with x, especially since x will not exist tomorrow," problem?  The treaty (contract) is with Poland, and there's a German answering at their number now...

I don't like having to pick on libertarianism.  It's sure a spiffy utopia; but it's got some blind spots you could hide Jupiter in.  For a philosophy to attain functionality it has to be practical in everyday use.  Libertarianism doesn't have an effect defense against a group opting out and ganging up on the neighbors one at a time.  They come pre-divided for conquer.  There is no mechanism for enforcing contracts beyond shunning the contract breaker; all you have to do is watch mutual friends after a messy break-up to see how this doesn't work and there's almost nothing of import at stake there.