a comment to 10 Hackers Who Made History by Gizmodo.
As DDevine says, Richard Stallman is no proponent of Open Source, but of Free Software. Open Source was forked from the Free Software movement to the great displeasure of Stallman.
He really does not like the term Open Source, because that implies that it is only about being able to read the sources.
Different from that, Free Software is about the freedom to be in control of the programs one uses, and to change them.