That's not a great example. The First Amendment per se does only apply to the United States. When States violate freedom of speech, the complaint will necessarily allege violations of First and Fourteenth Amendment rights. The Fourteenth Amendment incorporates the rights protected by the First, Fourth, Sixth, and Eighth (and some of the Fifth) Amendments, and applies those protections against State governments as well.
At the same time, it's not a terrible example either, since it's not immediately clear from the text of the Fourteenth Amendment what's incorporated and what isn't, and so it does require interpretation. But it doesn't go "far beyond the letter of the law." It goes far beyond the letter of the First Amendment, but not far beyond the letter of the First and Fourteenth Amendments.