As long as those sites curate according to their transparent terms of use these rules wouldn't apply to them.

I'd argue there's no such thing as "transparent terms of use" that wouldn't be open to legal challenge. Twitter and facebook have terms of use, they're as transparent as any other site in that regard.

Reddit has banned whole sub-reddits and shadowbanned others, Hacker news has human mods who make qualitative decisions to curate conversations on this site.

This hits every forum, every newsgroup, every site that has user generated content.

That's not at all how the law reads.

https://www.law.cornell.edu/uscode/text/47/230

(A) any action voluntarily taken in good faith to restrict access to or availability of material that the provider or user considers to be obscene, lewd, lascivious, filthy, excessively violent, harassing, or otherwise objectionable, whether or not such material is constitutionally protected;

Moderation does not have to be systematic, transparent, unbiased, or applied fairly.

The combined parts 1 and 2 of the "Protection for “Good Samaritan” blocking and screening of offensive material" mean that you are not responsible for the speech you host, but you can also not be compelled to host speech you choose not to host.