I started a thread a bit like this once before, and I think the
OP there still contains questions that I think are interesting. I don't really know what the answer ought to be.
As an addendum, this always reminds me of a
book by Lawrence Lessig which I read probably 20 years ago, or thereabout. That book was about copyright law and the constitution, but the first part lays out an interesting argument about the relationship between constitutional interpretation and technological change, and how changing tech exposes what Lessig called "latent ambiguities" in the constitution.
The prototypical example that Lessig describes is the development of precedent around requiring a warrant for a wiretap under the 4th amendment protections against unreasonable search and seizure. The point being that the framers could not have anticipated the interpretational question about whether or not a wiretap constituted a "search" or not, and so there's no completely objective way of trying to extrapolate a position on the question merely from the text.
Analogously, I feel like the internet and changes in communication technology certainly have created a world that is so different from the one the framers inhabited that it's not clear exactly how they would have thought about free speech if they'd lived today. It's not clear that the costs and benefits of various regimes aren't much different than they were. Particularly, the social costs of some kinds of speech seem potentially much higher just because mass communication is so much more efficient, both for traditional media entities and also via social media and the like. So I think that consideration at least makes it an interesting topic to think about, even if you're (rightly, I think) very cautious about restricting speech rights.
And to reiterate that it's not all about social media, I think it's worth asking what would the world be like if Fox News had always been held to higher standards of truth in its broadcasting by tighter regulations? I'm guessing that is more consequential to the state of American politics in 2019 than Facebook. I don't know if the tradeoffs would have been worth it, and I'm not saying there aren't also costs of regulation. But it's interesting.