Freedom of speech is quite a hot topic lately, and I believe it's important to outline two main thrusts of concern. The first is simply opposing various forms of censorship - "Twitter should ban X", "Youtube shouldn't regulate Y", etc. The second is infrastructural - that is, the development and deployment of infrastructure which can regulate and surveil speech. For example, Apple's recent move to scan every picture and message to evaluate if it is child pornography.
The first thrust - so long as it isn't the government curtailing speech - isn't really about legal precedent, and I'm not really concerned about it, at least not in the way a so-called Libertarian might be. This is because private corporations, owned by Capitalists, are dictators of their enterprises - they have supreme power over their dominion. The erosion of freedom of speech on these platforms is therefore not surprising; insofar as it is an assault on the "public forum", this is a failure of the government to properly establish a public forum, not a failure of Capitalist dictators to... be nice?
These assaults from Capitalism are nothing new either. Many many labor organizers have been killed and persecuted for their work for over a century. So am I surprised? No. I believe the right-wing virtue signaling about "freedom of speech" on private platforms is utterly naive, when in good faith, and insidious, when in bad faith. This brings me to my next point.
Freedom of speech is under threat only insofar as the infrastructure is in place to censor and surveil. For example, it is possible to curtail speech right now, to surveil the population (even without all that NSA stuff!), because the "public forum" is controlled by private dictators - there's no law, no Constitutional article or ammendment, preventing Youtube from taking down your video!
This is the key point I want to make - whining about "Twitter infringed my freedom of speech" is misguided. Of course they did, because they can. The only way to prevent this from happening requires de-commodifying the public forum. This means, as I suggest, a federated forum based on open-source and interoperable technology (a la email), or as others argue for, a government-regulated forum (a nationalized Facebook, if you will). Both of these approaches aren't perfect, but until one of them happens, there is no such thing as "freedom of speech" in the public forum to begin with.