Libertarians have differing opinions on the validity of intellectual property. Most left-libertarians<!-- , with some historical exceptions like Lysander Spooner and Henry George, --> oppose it whereas among propertarians/right-libertarians and libertarian parties there is more nuance, ranging from strong opposition to neutrality and support (particularly from those who are influenced by Ayn Rand's views).
Left-libertarianism
Most left-libertarians, dating back to Pierre-Joseph Proudhon (a libertarian socialist who is considered "the father of anarchism"), oppose intellectual property as part of their broad criticism of capitalism and anti-capitalism. Benjamin Tucker, a 19th-century American individualist anarchist opposing intellectual property, argued that "the patent monopoly consists in protecting inventors against competition for a period long enough to extort from the people a reward enormously in excess of the labor measure of their services,in other words, in giving certain people a right of property for a term of years in laws and facts of Nature, and the power to exact tribute from others for the use of this natural wealth, which should be open to all." Lysander Spooner, another 19th-century American individualist anarchist or left-libertarian who also influenced propertarians/right-libertarians,<!-- https://www.google.com/books?id=yyPEDwAAQBAJ&pg=PT2 --> argued strongly for patents, while Henry George<!-- https://www.google.com/books?id=3goqDwAAQBAJ&pg=PA94 --> distinguished between patents and copyrights.
Propertarianism/Right-libertarianism
Anarcho-capitalists oppose the existence of even a minimal state. This ideological framework requires that any functions served by intellectual property law promulgation and enforcement be provided through private sector institutions. Murray Rothbard argued for allowing contractually arising infinite copyright terms and against the need for any government role in protecting intellectual property. Rothbard states that government's involvement in defining arbitrary limits on the duration and scope of intellectual property in order to "promote the Progress of Science and useful Arts" is inherently problematic, saying: "By what standard do you judge that research expenditures are 'too much,' 'too little,' or just about enough?" Thus, he argued that intellectual property laws can actually hinder innovation since competitors can be indefinitely discouraged from further research expenditures in the general area covered by the patent because the courts may hold their improvements as infringements on the previous patent and the patent holder is discouraged from engaging in further research in this field because the privilege discourages improvement of their invention for the entire period of the patent, with the assurance that no competitor can trespass on their domain. Opponents to intellectual property rights include Wendy McElroy, Tom G. Palmer, Henri Lepage, Boudewijn Bouckaert, Jeffrey Tucker, and Stephan Kinsella. Kinsella observes in Against Intellectual Property that patents may be inefficient since they divert resources from research and development to patent filing and lawsuits. He writes that theoretical research can not be patented as easily as practical research and thus theoretical research is relatively underfunded. Moreover, he argues that property rights can only apply to resources that are scarce, which intellectual property is not. Kinsella also states that the only way that intellectual property rights can be implemented is by limiting others' physical property rights. David D. Friedman takes a neutral stance on intellectual property, arguing that "there are good arguments on both sides of that question". J. Neil Schulman instead argued in favor of intellectual property. In Capitalism: The Unknown Ideal, she wrote: