I know more about liberal theories of property rights than I do any other philosophical subject. I am not sure why, but I was fascinated by procedural accounts of the origination of property rights for a multi-year long span of time, during which I read just about every canonical text in the debate. Much to my delight then, I see Matt Yglesias and Bryan Caplan sparring over an esoteric property rights problem: if property rights are to be justified based on just procedures, then how can any they exist given that those procedures have not been followed. Backing up a bit, here is how this particular brand of property rights arguments are supposed to work. Initially nobody owns anything. Then someone grabs up a piece of the world and now owns it. From that point, voluntary trades are made indefinitely for that piece of the world. This process is said to be voluntary, non-aggressive, and non-coercive, and it is the following of this process that is supposed to justify whatever holdings exist at any given time. The problem of course is that we haven't followed this process, not anywhere close to it (see also Native Americans). In the debate between Caplan and Yglesias, the primary point of discussion is what exactly to make of this. Caplan -- as Yglesias rightly points out -- begs the question in the debate: he assumes that libertarian property rights are just and then constructs an ad-hoc policy to move forward despite the unjust origin of all existing property holdings. But whether you can come up with a policy to move forward or not is irrelevant. The debate is about whether a just-process theory of property ownership can explain why any existing property claims ought to be respected. It cannot do so because just processes were not followed. This remains true even if practical policies can be put in place that allow existing holdings to remain. But just-process libertarian theories of property rights beg the question in a much more fundamental way than Caplan does. The just-process theory of libertarian property rights basically works like this:

1. Economic processes are just if they are voluntary, non-coercive, and non-aggressive.
2. The libertarian process of homesteading followed by consensual trades is voluntary, non-coercive, and non-aggressive
3. Therefore libertarian process of homesteading followed by consensual trades is a just economic process

You can attack either premise one or premise two or both. I happen to think both are false, and that premise one is actually impossible in a finite world where scarcity exists. But I will leave that aside. The easier move here is just to point out that premise two is wrong. The libertarian process of homesteading is not voluntary, non-coercive, and non-aggressive. At time 1, nobody owns anything, and everyone can access any piece of the world. At time 2, someone has "homesteaded" a piece of the world. This homesteading is done entirely unilaterally. Everyone else in the world is not consulted; their consent is not provided. If someone from the set of "everyone else in the world" decides to take advantage of their previously existing access to the piece of the world that was homesteaded, what happens? Violence is acted on them. That is, aggression is acted on them. Libertarians typically respond that the violence mentioned here is not aggression: it is defense because the person owns the land. Wait a minute! That begs the question. The central question is: do you actually own the land? I am claiming you do not; and you are claiming you do. The way we are supposed to adjudicate that question is to ask: do the processes involved in you coming to own it involve aggression? The libertarian is saying he owns the land because he is being non-aggressive, and saying he is being non-aggressive (defensive) because he owns the land. The circularity is apparent. If I never agreed to the economic regulation that says "if a person homesteads unclaimed land, he may violently keep others from it for the rest of history," imposing that rule upon me is not voluntary. At an initial point -- according to the libertarians -- I have access to every piece of the world. I never agreed to forego that access. It is taken from me, bit by bit, through unilateral actors who use violence against me if I resist. The act of homesteading literally involves threatening every other human being on earth with violence. It says: this piece of the world is now mine, you may no longer access it ever again, and if you try to do so, I will physically assault you. The process of unilaterally stripping access away from every other human being on earth is clearly not voluntary, and involves coercive threats of violence. When those threats end up being acted out because a person does not go along with these unilateral proclamations of ownership, it is aggression. And the only thing libertarians ever do when confronted with that obvious reality is beg the question on ownership by assuming it already exists even as its existence is precisely what is in contention.