Separately, I think we should get big tech out of the business of acting as the public commons, but I don't think forcing them to apply promotion and editorial decisions without regard for the content itself is a good idea. We could force them to stop doing all promoting and editing, which would kill the platforms (good! I'm OK with that!) but that doesn't seem to be what these folks want. They already have that in the form of email, and they don't seem to think it's sufficient.
Imo, the next big argument will likely be whether there is a difference between a platform and a protocol as well.
To reference a provided example, the civil rights movement certainly benefited from freedom of speech, but at no point were mainstream media outlets compelled to publish opinions by civil rights leaders. While I'm pretty ignorant of the history, I'm sure the civil rights movement was largely organized and energized by alternative media - zines, newsletters and the like - and not by ABC news.
The arguments against free speech aren't really arguments based on any related principle or reason at all, because they are mainly just militating against people, and not engaging with ideas. They're not discourse. The alternative to discourse is violence, and attempts to suppress discourse tacitly advocate that violence.
The principled people who signed this delcaration have had the patience of saints so far, perhaps because they understand what the consequences are when it fails. I don't think there is anyone to convince or persuade anymore. Find each other, connect, and just cut out anyone who repeats the recieved narratives. Save yourselves, there's nothing you can do for them.