Via Ben Sheffner's Copyrights and Campaigns blog comes this passage from Justice Ginsburg, joined by six other members of the Supreme Court in the 2003 ruling Eldred v. Ashcroft:
Justice Stevens' characterization of reward to the author as "a secondary consideration" of copyright law, post, at 6, n. 4 (internal quotation marks omitted), understates the relationship between such rewards and the "Progress of Science." As we have explained, "[t]he economic philosophy behind the [Copyright] [C]lause … is the conviction that encouragement of individual effort by personal gain is the best way to advance public welfare through the talents of authors and inventors." Mazer v. Stein, 347 U.S. 201, 219 (1954). Accordingly, "copyright law celebrates the profit motive, recognizing that the incentive to profit from the exploitation of copyrights will redound to the public benefit by resulting in the proliferation of knowledge…. The profit motive is the engine that ensures the progress of science." American Geophysical Union v. Texaco Inc., 802 F. Supp. 1, 27 (SDNY 1992), aff'd, 60 F.3d 913 (CA2 1994). Rewarding authors for their creative labor and "promot[ing] … Progress" are thus complementary; as James Madison observed, in copyright "[t]he public good fully coincides … with the claims of individuals." The Federalist No. 43, p. 272 (C. Rossiter ed. 1961). Justice Breyer's assertion that "copyright statutes must serve public, not private, ends" post, at 6, similarly misses the mark. The two ends are not mutually exclusive; copyright law serves public ends by providing individuals with an incentive to pursue private ones.
This is one useful way to think about the profit motive, not only in connection with copyrights, but lots of other things. There are at least two other ways. One is that authors and inventors would have a right to the fruits of their labor even if it didn't serve public ends, because it is their property, and everyone has a right to their own property; it's a natural right recognized in the Ten Commandments' prohibition against stealing. Second is that it's an overstatement to say that the profit motive is the engine of science; plenty of scientists are motivated by things other than profit, including intellectual curiosity, the desire to cure or prevent disease, and the desire to win the respect and acclaim of peers.