From Libertarian Wiki

There are many arguments you can raise against intellectual property:

• The distinction between protectable and unprotectable ideas is arbitrary. For instance, philosophical, mathematical or scientific truths are unpatentable, despite the fact that labor was exerted in discovering them. This encourages research into practical applications of ideas rather than into "pure" scientific research. Yet the practical applications rely on the laws of science and math.
• The terms of patents and copyrights are arbitrary. Who is to say that politicians know best how to strike a balance between rewarding innovation and stifling future generations?
• Intellectual property rights, to be enforceable, must override tangible property rights. An IP owner becomes a partial owner over others' tangible property by virtue of the fact that they may not use that tangible property in a way that infringes the patent. E.g., if someone patents a new method of drilling wells, your right to do what you wish with your land is no longer absolute because you may not drill a well in a way that infringes the patent. IP law trespasses against and takes the property of tangible property owners, by transferring partial ownership to authors and inventors.
• Property rights only make sense when applied to conditions of scarcity where conflicts can arise. If lawnmowers, for instance, could be conjured up out of nothing in the blink of an eye, then my taking your lawnmower would not a violation of your property right, because no conflict would arise. Similarly, my use of your patented technique for, for example, making cotton does not deprive you (or anyone else) of the ability to use that same method. Accordingly, there is no basis for a property right in intellectual property.
• Who is to say that invention, writing, etc. should be artificially encouraged more than, say, farming or construction? Is there really any basis for believing that no new drugs, electronic devices, etc. would be invented in the absence of intellectual property rights; or that no new books would be written? The burgeoning open source software movement and the success of volunteer projects such as Wikipedia would seem to refute this.

Pertinent essays

• Against Intellectual Property