You'd have to explain that to Richard Stallman, who wrote the GPL and also sold Emacs and other free[1] software commercially during the 80s and 90s.
[1]: free software and open source software are accepted by the Free Software Foundation and the Open Source Initiative as being pretty much the same thing (ie 99% of OSI-approved open source licenses are also FSF-approved, and vice versa).
[1]: free software and open source software are accepted by the Free Software Foundation and the Open Source Initiative as being pretty much the same thing (ie 99% of OSI-approved open source licenses are also FSF-approved, and vice versa).