Turns out that Proudhon, the socialist mutualist anarchist and critic of capitalism, was in favor of monopoly after all–in particular, patent and copyright. See pp. 8-9 of Machlup & Penrose, “The Patent Controversy in the Nineteenth Century” (1950). Sad.
Update: per the comments below, Shawn Wilbur says Machlup got this wrong: that Proudhon was not in favor of any form of copyright or patent at all, and that Machlup is misconstruing what Proudhon meant by his use of the word “necessity”. Interesting. Wilbur has pointed me to this English translation of the text Machlup was citing. I am taking a look at it and cannot verify Wilbur’s claim, but it does seem credible.
Update: See also quote of Proudhon in Locke on IP; Mises, Rothbard, and Rand on Creation, Production, and “Rearranging”.