> I suspect most of the commenters supporting the right of a private company to moderate content is completely contingent on what those moderation policies are.

I'm one of those commenters, and I'd point to Gab, Parler etc as companies who are already doing exactly that and are well within their rights to do so. And of course, their free speech (curation and flagging) is balanced by their users' freedom of association: if twitter radically changes their moderation policies, they could risk driving away their userbase and even their developers.