That is a awesome Wiki link. I know Kshartle hates outside sources of ideas, but these few paragraphs that challenges the NAP were perfect:
Critics point out that almost every patch of land on Earth was stolen (i.e. obtained through initiation of force) at some point in its history. The stolen land was later inherited or sold until it reached its present owners. Thus, property over land and natural resources is based on the initiation of force. Among those who make this argument, some claim that private property over natural resources is unique in being based on the initiation of force, while others hold that, by extension, private property over all goods derives from violence, because natural resources are required in the production of all goods.[citation needed]
Some supporters respond with the "water under the bridge" argument: transgressions of the past cannot all be rectified, and that an act of theft which happened long ago can reasonably be ignored. Critics argue that this implies that peaceful possession of property in the present legitimizes theft and/or trespass in the past. This requires a "cutoff" point: a point in time when illegitimate property becomes legitimate property. Some critics argue that any such point is arbitrary. Some supporters respond that property can only have a legal owner as long as there are no conflicting ownership claims to that property. The “cutoff”? point, therefore, is when the owners whose property has been stolen drop their claim because property that has no ownership claims at all is free for anyone to homestead.[citation needed]
Many libertarians support the idea that only labor creates ownership (see the labor theory of property). Some hold the position that land and all natural resources are not man-made and therefore cannot be owned. Others believe the community is the owner and that people should pay rent to the community for land they use (see Georgism). The homestead principle allows land and other natural resources to be privately owned.
Political theorist Hillel Steiner emphasizes that all things made come from natural resources and that the validity of any rights to those made things depends on the validity of the rights to the natural resources.[75] If land was stolen then anyone buying produce from that land would not be the legitimate owner of the goods. Also, if natural resources cannot be privately owned but are, and always will be, the property of all of mankind then NAP would be violated if such a resource would be used without everybody’s consent (see the Lockean proviso and free-market anarchism).[76] Libertarian philosopher Roderick Long points out that, as natural resources are required not only for the production of goods but for the production of the human body as well, the very concept of self-ownership can only exist if the land itself is privately owned.[77]