I don't actually think it's more nuanced than that because the constitution is pretty explicit about "free speech" and the founders certainly weren't advocating that publishers have to publish things they didn't want to publish so maybe you can do us all a favor and explain where you think the nuance is as opposed to just suggesting it has to be more complicated than that.
Lets say we have a company that pays politicians to do what they want, this is what you call free speech. This company also has the power to silence peoples voices on the public forum of that day, this is what you call free speech. Do you think this is what the founders intended by "free speech"? I do not, these two together means that the line between government and big corporation gets blurred, and that now effectively the people who decides what gets legislated are also the people who are free to censor people.
The founders didn't intend anything for "free speech" save for what they enshrined in the constitution. I'm not sure how that could be more clear. Facebook is not a public forum. Back in the founders time, the only public square was the actual public square. There were even fewer publishers with even fewer opportunities for people to have their ideas amplified and disseminated, and even back then they did not think that xyz printing press had any obligation to publish anything anyone wanted to.
