Open source as defined by the OSI which is what most people agree with, is exactly identical to what RMS calls free software. RMS wants open source to mean what most people call "source available".
We have the terms source available and open source which are well understood and has no ambiguity but RMS and the FSF want to push their free software term and have to change open source so their term isn't obsolete.
It's nothing to do with being a purist or ideal. Because the wider understanding is exactly as pure and ideal. They just aren't the words RMS wants us to use for those meanings. He is obsessive but not for any real gain.
