Yes. I don't intend to say that
no one should be able to organize their forums or exclude some speech; doing so is a critical part of maintaining something functional and workable.
We don't have to fling to one extreme or the other. There is a moderate position here. And remember, this is about the importance of free speech as a social principle. If we don't cherish our rights, they'll vanish. I'm not necessarily advocating any specific legal changes.
HN is a boutique site that targets a specific niche. I would guess it has a few thousand active users. It's developed and designed specifically to facilitate discussion on issues that fit its niche and target audience.
Facebook, Twitter, et al, on the other hand, are platforms that function much like public utilities. They are used by the masses to disseminate speech of all kinds. They target a generic user base and suggest that they can all use the site to follow their individual interests.
Beyond the mere target audience of "everyone", Facebook and Google have massive amounts of control. The penetration of Google and Facebook is probably almost exactly equal with the penetration of internet service (and to some extent, both have projects that take them beyond that sphere). If you use the internet, the likelihood is that significant amounts of your usage are under the direct control of these corporations.
Facebook boasts over 1 billion daily active users. That is 1/8 of the earth's population. That is MASSIVE -- far further reaching than any monopoly in the pre-internet age. Facebook is also the platform that people depend on most heavily for self-expression. It's a central hub that many people visit multiple times each day; some groups and businesses are now run entirely out of Facebook. Functionally, it is not unlike the pre-internet public square, and it's a frequent crossroads for almost all internet users. As with past public squares, it's possible to avoid it if you're trying really hard, but you essentially have to be a digital recluse.
This applies similarly to Google for search, email, and mobile.
As such, it's scary when such powerful platforms that present with such generic mission statements and see such widespread adoption start erasing political speech because they deem it "offensive" at the corporate level.
That is a ridiculous amount of control, and it's something we've never experienced before. Even the broadcasters of the 20th century were limited by the reach of radio waves to specific metros, and they usually had several easily accessible competitors (that people would actually use, unlike FB's direct competitors). We used to worry about the large influence of these people so much that it was illegal to own more than a certain number of major media outlets in the same market (that restriction was removed in 2003, IIRC). [We also used to have the Fairness Doctrine to compel broadcasters to accurately present both sides of the political issues.]
People recognized the damage to the public square posed by moving the discussion off to corporate-controlled broadcast media and wanted a way to check the power of the broadcasters. We seem to have forgotten about that risk, just at the moment when the central control of a small handful of people is most potent.
Imagine that printing press manufacturers had the ability to stop press owners from setting certain things to the page. That reflects the reality of the publishing mediums we depend on today. That should be worrisome.
I'm stopping short of suggesting a legal solution, but just speaking to this as an important social principle, we should all be disgusted with the conduct from the major online platform providers. Such general, widely-used platforms are betraying the public and our principles and values in favor of open dialogue by working to distort the landscape of public opinion and curtail the speech of the political, philosophical, or moral enemies of the corporate overlords.