Property Rights ?
One might imagine that property rights are human rights, natural rights, pre social rights like the right to freedom of speech. In this view, very well expressed by Locke, laws which violate property rights are unjust laws, bucause property rights are not established by laws but are rather recognised or discovered by just laws.
Another view, which I first read in "Just and Unjust Wars" by Michael Walzer is that property rights are only rights under the law and that different systems of property rights are to be judged by their consequences, that is as instruments. Shame on me for not having thought of it, but it seems obvious once it's mentioned that there are two kinds of rights natural rights and rights under the law, and that I personally agree with him that there are no natural property rights except as required to protect natural rights (it violates the moral law to seize printing presses because one doesn't like what was printed on them or to declare someone's car to belong to someone else ex poste facto and arrest him etc etc).
A third view is that property is theft and that alleged property rights do not and can not exist whatever is written in the law. The third view is not very popular these days and I won't discuss it further.
I think that, to this day, the best argument for natural property rights is due to Locke. Locke's argument is clearly invalid. He starts from assuming that we own ourselves and the fruits of our labor. He bases this on a very forced reading of a line in the old testament. There is no argument there of interest to people who don't accept the bible as authoritative. For this reason this claim is not contested. I think it is obvious that people do not have a natural right to the fruits of their labor, because this implies that it is just and fair to allow the unfortunate disabled to starve. To me rights must be equal and so one can not have the right to more because one was fortunate to be born able. Only if ability is the result of choices would I even consider the fruits of one's ability to be posessed by natural right. This would, of course, just shove the problemm back one step, since, for example, one's choice to learn a skill depends in part on ones ability to learn it and that depends in part on luck.
I think the claim that we have a natural right to the fruits of our labor is simply false. For the sake of argument I will concede it.
The problem for Locke is that, according to the existing laws, which he aimed to prove to be human rights, people owned things that they clearly did not produce, in particular land. Since Locke was aiming to advance the claims of the house of commons over the claims of the king, he had to focus on land ownership, since, when he wrote, the house of commons represented land owners. If there were a natural right to some property but not land, the house of commons would have no claim to rank above the tailors guild let alone the king.
Thus Locke claims that most of the value of land is the value of improvements in the land so that the value of unimproved land is neglegible. Here we see that Locke wrote before the dawn of economic theory. To anyone who keeps track, the claim is absurd. More importantly the relative value of unimproved land and improvements on land can not be the basis of a claim about human rights or natural law, since relative prices are clearly contingent on supply and demand. This was true in Locke's time. He simply chose to ignore this fact, that is, to lie.
Worse for Locke, he can explain how there might be a right to homestead so long as there is plenty of unimproved land available "as much and as good" but he refuses to notice that this can not in any way justify current land ownership. This is obvious. There was not "enough and as good" in England in 1683, therefore the last act of homesteading was imoral. But this means that no one could homestead after the second to last act of homesteading so there wasn't enough and as good after that and so by backwards induction all claims of property in land are, according to Lock, imoral.
Here I think he might have a real intellectual problem. I think he did not consider other legal institutions that freehold. For example, one could imagine a contract between a person and society in which society gives that person exclusive use of some land so long as there is enough and as good and, in exchange, the person allows society to redistribute the land with improvements when there is no longer enough and as good. This could lead to a distribution of rights to use land based on the scriptural principle that people have the right to the fruits of their labor so long as they don't sell them forward.
The principle of enough and as good does not imply that one has the right to land forever if there was enough and as good when you settled on it, thus it can not serve Locke's purpose.
Of course Locke new perfectly well that current land ownership had nothing to do with improving land and everything to do with being a decendent of an officer in the army of William the conqueror so the whole thought experiment is a utopian fantasy.
Now I might be wrong, it is possible that someone has come up with a better argument for the claim that there are natural property rights which are recognisably similar to current property rights under the law, but I doubt it, since Locke is still quoted.
I think the emotional power of the idea of property rights is (see post below) based on a failure to accept a difference between rights under the law and natural rights, so existing laws or laws from a century and a half ago are seen as descriptions of natural rights which can not morally be eliminated.
Also, I think, people switch back and forth between arguments based on respect for rights and consequentialist arguments without noticing. That is, a reasonable defence of existing property rights is that with such rights we have a prosperous society and countries which tried something very different ended up very poor. If one asks people to imagine a world in which collective ownership say leads to prosperity and decide if it would be just or unjust, they become irritated. Most people find the question of whether a law is a good instrument towards an aim or an expression of natural rights totally boring.
This it certainly is, but sometimes a refusal to consider the question leads to nonsense (see the post below).