The natural state of things is that nothing is owned. It is for those who would assert ownership over resources to justify their claim, not for those who would challenge the claim to justify their challenge. This is not to say that such claims are incapable of being justified; it may well possible for an owner to present a compelling case to justify his ownership; however the burden is on him to prove his case. The assumption in all cases is that resources are not owned.
Claims of ownership rest on one of five circumstances, or some combination of them: inheritance, purchase, gift, a grant of ownership from a legal government authority, or appropriation by force. In the first three cases the person or persons bequeathing, selling or giving the property must themselves be legal owners of the property similarly legally obtained by one of these five actions, and so on back to the very first owner.
There must have been a first owner, since there was unquestionably a time in the past when nothing in the world was owned, because ownership itself had not been thought of. This does not mean that the lands were not occupied and used, it just means that nobody had thought of asserting the exclusive right to a piece of land or the right to charge others for the use of it. No doubt pre-agricultural humans, like other animals, would establish territories, but they only occupied them to the extent that they could physically assert their right to do so. They did not think the land belonged to them exclusively.
What, then, was the first owner’s legitimate claim to the property, which started this whole chain? This person could not have received it by any of the first four methods, or he (I am betting the very first owner of anything was a he) would not be the first owner. That only leaves appropriation by force, or what we would call today armed robbery. We can rule out number four, a grant from an established government, as this must have taken place before the first established authority structure; in fact the first assertion of ownership must have created the need for the means of enforcement of property claims. The only point of asserting ownership of something is to prevent others from using it unless they pay you. Naturally people who had always traditionally used the land would angrily resist such an assertion, and so the putative owner needed muscle, and so the whole control system begins.
The inevitable conclusion we must reach is that all property rights are illegitimate from the very start. Now I realize that this argument would probably not get very far in court, but this does not mean it is not correct. It just means that some things that are correct bring with them so much uncertainty and fear of deep rooted change the even those who stand to gain the most by it cannot be brought to support them, let alone those who actually make the decisions, who have much to lose from large scale change.
This may not always be the case. Ideas and attitudes die with each generation, and a time will come when it becomes quite obvious that allowing a minuscule class to continue to rule over everyone by simply asserting their right to do so is quite ridiculous. Therefore it seems important to lay the ethical groundwork for this realization.