Free speech is a very well defined concept, as done by literally hundreds of political science scholars. The fact that the US Constitution applies it only to the Government does not mean it cannot be discussed in a different context. For instance I would like new regulations to extend free speech outside the scope of the First Amendment. This is an extremely well defined politica stance.
You seem to agree that Twitter is NOT a common carrier, and then it must be treated as an editor. This would imply that they are responsible for the tweet they decide to publish.
These are exactly the far-reaching legal ramifications of free speech (outside Government) that I was mentioning.
People can discuss things that are not law.
One can point out, for instance, that Twitter is not a free speech platform, and this is bad for many reasons.
One can comment on laws, proposing to extend legal protections to different sectors.
I hope your conversations are not solely based on current law, that must be pretty boring.
(You interpretation of Section 230 is shaky at least)
Edit: Note - I am not blaming you for the communication breakdown, it seems that perhaps we were both coming at this from different sides and may have missed each others points. Either way, wish you all the best.