Stephan Kinsella at Mises.org says he detects a belief in and defense of intellectual property fading among libertarians--and he thinks that's great. He traces the documents and thinkers that lead him to this belief, hits at the supposed utilitarian arguments for IP, and gives some reasons why libertarians ought to abandon intellectual property:
The mistake made by IP libertarians stems in part from the imprecise, overly metaphorical Lockean notion that the reason you own things you homestead is that you "own" the labor you "mixed" with these things — rather than the more straightforward argument that by first appropriating an unowned resource you establish a better claim than latecomers — no fiction of "labor ownership" is needed (see "Intellectual Property and Libertarianism"). This mistake permeates the modern — mostly Randian — thinking about IP. This way of thinking about homesteading, and the American Founders' choice to put copyright and patent in the "protolibertarian" American Constitution...and Rand's and others' adoption of these ideas, has created a road block to clear thinking about IP.
They say that you own things you find (appropriate or homestead) and things you buy from others — and "also" anything you create. They miss the fact that finding and contractual acquisition exhaust the ways of legitimately acquiring ownership of external objects. "Making" or "creating" simply refers to the process of transforming something you already own by rearranging it so that it is more valuable to you, or to a customer, say...Creation isnot an independent source of ownership; it is a way of making your property more valuable. (See "A Theory of Contracts: Binding Promises, Title Transfer, and Inalienability"; Against Intellectual Property, "Creation vs. Scarcity" section; "Objectivist Law Prof. Mossoff on Copyright; or, the Misuse of Labor, Value, and Creation Metaphors"; "Libertarian Creationism." "Trademark and Fraud")
By assuming the "ownership" of labor, even though the ability to control one's actions and labor is simply a by-product or consequence of ownership of one's body..., and not an independent property right; by assuming that creation is an independent source of property rights, even though it is not; by assuming values are created, ownable things, rather than the changed utility of property the owner himself rearranged — these libertarians have equated nonscarce ideas and patterns with physical, scarce resources. After all, by your effort or labor, you create a plow, a house, or a song, right?
By treating these dissimilar things — nonscarce, infinitely reproducible patterns of information and physical, scarce objects — similarly, the IP advocates try to treat them with the same rules. They take property rules designed precisely to allocate ownership of scarce physical objects in the face of possible conflict and try to apply them to information patterns. In so doing, they end up imposing artificial scarcity on that which was previously nonscarce and infinitely reproducible.....
And what does IP do? In the name of capitalism and the free market, it imposes artificial scarcity on things that are already infinitely reproducible. In the name of the market — the same market that is working to increase the abundance of scarce goods, to decrease scarcity — IP libertarians argue that we should impose restrictions on nonscarce information — to make it scarce so that it fits into the round-hole property-rights framework they have erroneously decided to apply to the square peg of information.
Kinsella seems to be giving a utilitarian spin on what to most pro-IP libertarians is a moral case for ownership of those things you produce; I think most pro-IP libertarians would simply deny his contention that creation is not an independent source of ownership; indeed, it may seem a far purer and less problematic form of establishing just ownership than homesteading the existing physical world.
Such libertarians might say, who the hell cares about imposing artificial scarcity if you are defending justice? Land ownership is seen by many non-libertarians (and even some 19th century libertarians) as itself imposing an artificial scarcity when said ownership is divorced from occupation. Still, Kinsella's piece and its many links are a good guide to how a Rothbardian pro propertarian libertarianism can come to anti-IP conclusions.