Law professor, writer and political activist Lawrence Lessig, along with many other copyleft and free software activists, has criticized the implied analogy with physical property (like land or an automobile). They argue such an analogy fails because physical property is generally rivalrous while intellectual works are non-rivalrous (that is, if one makes a copy of a work, the enjoyment of the copy does not prevent enjoyment of the original). Other arguments along these lines claim that unlike the situation with tangible property, there is no natural scarcity of a particular idea or information: once it exists at all, it can be re-used and duplicated indefinitely without such re-use diminishing the original. Stephan Kinsella has objected to intellectual property on the grounds that the word "property" implies scarcity, which may not be applicable to ideas.

Who is one advocate of copyleft?