If twitter/facebook is allowed to serve as a primary means for an government organisation/department to serve as the primary way which it communicate it's not to hard to argue that that line have been crossed where it have to act as an "open access" common carirer, from an pragmatic real world stand point.
Putting an purely technical definition as the core of this debate is arguing over how many angels can fit on an pin needle, and not of any real value for deciding what kind of society we want.
Twitter et al. are where modern speech happens. They pushed themselves into this position, and thus upholding the human right to free speech also falls upon them.
So long as Twitter is not shut down, then perhaps some government oversight (to the limit of holding Twitter responsible for what and who they censor) is appropriate.
Free speech, in this case, trumps my intense dislike of our current administration.
Where is this in US law? Are you confusing DMCA safe harbor issues with speech?
All platforms take control over content - otherwise they could not remove child porn, PII, etc., and they don't lose DMCA safe harbor exemptions, which only applies to copyrighted items posted by users.
Applying this to Twitter, Facebook et al. is not that big of a leap.
> completely destroys the business model of several hundred billion dollar businesses
They are not entitled to their business model, especially not at the price of trampling upon something broadly considered to be an inherit human right.
Except they are held responsible if they don't curate. Look at laws like SESTA to see how platforms that don't self-curate content that could sexualize minors are legally liable.
I'm not saying SESTA is bad, I'm saying this idea that platforms need to be hands-off towards curation to maintain safe harbor protection is not true.
Your idea that safe-harbor laws only apply to platforms who don't self-curate is absurd precisely because there is illegal content they, the platforms, can be held liable for instead of the users.