(which wouldn't happen because families work together to help each other, that's part of the point)
Here's the problem, people don't enter the world with zero debts to society. Infants cannot provide for themselves at all, not even when it comes to eating, so these children owe a debt to their caretakers. However, their caretakers owe a debt to the forces of civilization that protects them from violence and that ensures the operation of some type of economy. If armed gangs of thugs run around disrupting life, it is hard for families to provide for their children.
However, I'm sure that you will make a point that families can arm themselves to ensure their own security. It's true they can, and in many cases it will work. The thing is, this forces them to devote far more resources to get equal or less protection than society could provide for them. You will say that Libertarianism isn't anarchy, because it has courts, police etc. Yet who pays for this and how? It's hard having it both ways, that society still provides all of the comforts we as a people have grown found of, yet we pay nothing.
So who pays, and how do they pay? What would a Libertian society provide?
EDIT: Though I think we need MAJOR changes to society as well. I'm all for social Libertainism, but I think that full blown Libertarianism wouldn't work, that it would break down either into Anarchy or a Corporate dictatorship. I guess in the same way that socialists are communist-lites, I'm a Libertarian-lite. However, if you can ever provide me with some kind of structural safeguards from the depreditations of organizations that aren't governments, then I would become a full blown Libertarian.
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