Entrusting our speech to multiple different corporate actors is always risky. Yet given how most of the internet is currently structured, our online expression largely depends on a set of private companies ranging from our direct Internet service providers and platforms, to upstream ISPs (sometimes...
I think the problem that poster was trying to illustrate is that it is unpractical to shut down a site or force a site to spend a significant overhead just cause a user could post a certain sequence of bytes to the site. An analogy to the real world would be some guy paints some graffiti on the pavement and the response, every time, being the complete shutdown of the entire city for a month or complete surveillance on every cm2 of pavement plus cleaning crews standing by every 10m.
Poster does not want his favourite site going down cause of some bad actor.