There’s a concept in economics that litigation is a public good: it’s how we figure out how the law works (or doesn’t) in practice and it’s why our courts are publicly funded institutions; moreover, we all benefit from it. Another concept known as “free-riders”, people who benefit from a public good without paying into it, is generally applied to the concept of supporting legal work: if litigation (as a public good) would likely generate case law that would benefit everyone in a state (say by a nominal $100 amount), then everyone should voluntarily pay the litigating party $100. Of course this is pretty rare. We see the same behavior with open source software licenses, legal documents which provide developers and end-users certain rights. Since these licenses’ provisions ensure universal access to the software (implying they are non-excludable) and don’t restrict public use of the software by end-users (making them non-rivalrous), these licenses can be seen as public goods.
Although tacking a license onto your project is “free”, each license can be modeled as having an associated cost: the cost of litigation to enforce the license’s provided rights. Permissive licenses like the MIT, ISC, and BSD licenses have a negligible cost of litigation because they essentially waive all rights to the source code of a project. You can’t sue to enforce rights you don’t have! The GNU General Public License (GPL), on the other hand, would have a comparatively high cost of litigation because it protects against a litany of things—the distribution of source code under licenses other than the GPL, the misattribution of the software’s original authors, and the obfuscation of source code to name a few. Clearly the more rights you have, the more expensive your license is to enforce. Detractors of the GPL frequently argue that some version of the free-rider problem necessitates the Free Software Foundation and other’s legal apparatuses which by virtue of that same problem must have their hands tied. Put succinctly, why bother with bureaucracy when you can just use a more permissive license? Nevertheless, permissive licenses—though they have their place—throw their hands up at the free-rider problem and generally ignore their role as a public good, basically writing maligned megacorps’ code for them; they aim at freedom in software development, not at freedom in the public’s use.
Of course any permissively licensed project is neither rivalrous nor excludable, but it can be copied wholecloth into something that is. The GPL maintains its state as a public good in all licensed projects and their derivatives.