"Free" vs. "open source" is a distinction without a practical difference. It's not about what it is or what it does, it's about vibes.
There's no future step of "popularizing it". They've been trying for 40 years and it's been an abject failure. Another decade isn't going to finally get it to stick, it's just a dumb idea. It's is a very up-their-own-asses grognard thing to just reject reality and keep demanding it happen. "Could it be that I am wrong? No, it must be everyone else who haven't just done what I wanted them to do because I told them to."
And yeah, "open source" and "source available" have some confusion, but that's at least a battle that can be won, and in most cases if you call a source available software package (an actual package with license terms, not just every github project) "open source", you'll usually be right (source available and not open source is already a minority). Pointing to that like it justifies instead continuing the crusade for "free" isn't even remotely comparing issues of similar difficulty.
Trying to jump in whenever someone calls costless software "free" with a "free as in beer"/"free as in speech" explanation or "no, that's costless software, not free software" just makes FOSS look like an arcane and exclusionary movement for unpleasant nerds, like Richard Stallman.