Nor again, can even the enforcement of contracts be fairly said to be a realisation of freedom; for a man seems, strictly speaking, freer when no one of his volitions is allowed to cause an external control of any other.
Henry Sidgwick, in The Method of Ethics.
It is often assumed by defenders of largely unregulated private property that theirs is the system that takes liberty the most seriously - indeed the system with the most freedom of agency. On the other hand, some are pure consequentialists and are ostensibly disinterested in liberty except as a tool to maximise utility. However most are not, and even those who claim to be often use highly loaded language with respect to their positions, perhaps revealing non-consequentialist intuitions. Milton Friedman for example claims to be a consequentialist libertarian (here, 1:45 minutes in,) however, for example, his most famous book is called Capitalism and Freedom (as opposed to, say, 'Capitalism and Happiness'). This is to me hardly the mark of a pure consequentialist. That is a topic for another post, however.
However I think many people forget to consider the flip-side, that private property is in itself a highly coercive institution. This is highlighted in the Sidgwick quote given at the start. Consider two situations. In Country A, the Government passes a law prohibiting people from boarding trains on Sunday. This is obviously a restriction on people's liberty, presuming that they were choosing to board trains on that day previously. In Country B however the Government is more laissez-faire and makes no such law. Despite this, the owner of the trains decides that in accordance with his religious principles, his trains will not run on Sunday.
From the perspective of the passengers of the train, the situation is identical (assume that the citizens themselves have identical demand for the trains between the two countries). They would like to ride the trains and are unable to do so because someone has told them that they cannot.
It seems to me that it is inconsistent to claim that one of these situations is an abrogation of liberty and one is not. Perhaps in B less liberty is violated, because in A the Government places restrictions on both the customers and the owner, while in B only the customers are so restricted (as the owner is free to sell tickets whenever he likes). However my general claim (and also Sidgwick's) if were actually concerned with the maximisation of individual liberty, we would not support the institution of private property. Indeed the very principle of private property is that the owner of the property is permitted to restrict the liberty of others to do what they want with it! The case can be drawn even more clearly by considering ownership of land. Are we really expected to believe that it makes a difference to liberty whether an individual or the Government tells us not to travel on a particular area of land?
The key thing to draw from this is not that we should abolish private property, it that there are such things as legitimate restrictions of people's free choices. I believe private property to be clearly one of them. Thus the goal of liberty maximisation is a misguided one, at least as it is crudely understood by many. This is hardly a killer blow to libertarian philosophy - for example Robert Nozick was one of the most vociferous critics of the idea, critiquing it as a 'utilitarianism of rights'. But we should be sceptical of, dare I say it, the Ron Paul libertarians, who claim to opposed to the initiation of force in all circumstances, but in supporting private property support one of the greatest initiations of force there is.
Update: Edited the post slightly for clarity.