The Constitution would not provide a carveout for the long-term censorship of a forum like KF based on some rationale like "creating a volatile atmosphere", so I don't know what you expect regulation to accomplish here. And of course activists would scream if such regulation were applied in a viewpoint-neutral fashion (eg. platforms being mandated to delete content that advocates for crime / violence - imagine how Trump would've used this power during the BLM riots!) - the non-neutrality is considered a feature of private censorship, not a bug.
Yes, well, that's the beautiful thing about common law - we still have a pretty clear understanding of what constitutes free speech, and it's largely invariant to whether the means of communication is through the internet or a medium that was more-familiar to the founders.
