This discussion is specifically scoped to the legal system in the United States. If you, as a US individual, express the opinion that "I do not like post with

This discussion is specifically scoped to the legal system in the United States. If you, as a US individual, express the opinion that "I do not like post with unique ID X on platform Y because of reasons a,b,c", that would be protected speech. A moderation feed would be equivalent to a series of such statements. If other users decide to subscribe to your moderation feed, and have matching posts automatically hidden, that would specifically be the choice of that individual user, and not a private company. One of the greatest scams governments around the world have managed to pull is making "free speech" a politically partisan issue. There are two sides to it though, but it's not conservative vs. liberal, it's the common people vs. governments and corporations.