http://en.wikipedia.org/wiki/Natural_law
The basic idea is that good laws are things we discover rather than create. Their form is dictated by the form of our being and intellect and the shape of our world. Any enforced law that contradicts this natural law will create the sort of friction and injustice that we would have seen with SOPA.
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Edit #1.1: As others have pointed out on this thread, the idea of owning non-scarce and easily-spread things is unnatural. So if technology makes a previously containable and scarce thing non-containable and non-scarce, then our ideas about what exactly can be property will change without having to believe that natural law itself had to change. This is the essence of Paul's argument, and why it fits with natural law theory. Technology changes the shape of our world.
Edit #2: All modern natural law thinkers I know of would assert that slavery always violated natural law in perhaps the worst way possible, so I don't see how Paul's concurrence that ending slavery was a good change in property law distances his position from natural law theory. It was always unnatural, and eventually we discovered and corrected that in our statute laws, prompted largely by the growing friction our divergence from natural law was creating.
Edit #3: There are various schools of natural law. My definition of it goes along the lines of, "the rules that humans living in a particular environment, starting with no preconceived notions, would voluntarily and near-universally adopt for their mutual benefit." If you're from a school that believes natural law exists without any reference to our environment, then you may disagree with my premise and everything that extends from it.