GPL ensures freedom for users of the software, not developers of the software -- a distinction that is missed every single time licensing is discussed. Developers that use the GPL are (hopefully consciously) making a choice to ensure software freedom for their users.
This article did a very good job of tackling this this from another perspective, by addressing the usual (and tired) argument that the GPL offers less freedom than more permissive licenses due to the share-alike clause. Limiting "power" to take away freedom is a nice way to put it.
Not to derail this discussion, but my personal opinion is that the GPL is a bit ahead of its time. With the marginal cost of software being nil, the path of least resistance is just to make software free. The problem is, someone still has to produce this software, and unless we hit post-scarcity, production is going to cost money [1]. So the GPL straddles an awkward tension between ideals and economic reality right now. This is in addition to the more overt goals of FSF/GNU in terms of privacy, control and self-determination, which RMS has proven to be quite prescient about.
[1] "In the long run, making programs free is a step toward the postscarcity world, where nobody will have to work very hard just to make a living. People will be free to devote themselves to activities that are fun, such as programming, after spending the necessary ten hours a week on required tasks such as legislation, family counseling, robot repair and asteroid prospecting. There will be no need to be able to make a living from programming."
https://www.gnu.org/gnu/manifesto.html -- a very good read.