In other words, let's keep the first amendment at the federal level where it was.
Are you saying that Congress cannot pass a statute (law) to prevent this type of "speech"? Why do you think that? The USSC wrote in Gitlow, "By enacting the present statute the State has determined, through its legislative body, that utterances advocating the overthrow of organized government by force, violence and unlawful means, are so inimical to the general welfare and involve such danger of substantive evil that they may be penalized in the exercise of its police power. That determination must be given great weight. Every presumption is to be indulged in favor of the validity of the statute."
If the USSC ruled that a state could write such a statute, why do you think they wouldn't have allowed Congress to write one? In other words, Gitlow would have been denied his brand of free speech whether it was a state or a federal law.
I think that you are correct about the Supreme Court at the time and I believe that the Supreme Court was wrong at the time.
I believe that the very understated way in which "incorporation" tool place was to avoid the very strong language that "Congress shall make no law ...". This language is about as strong as it can be. CFR is so obviously unConstitutional because of the fact that Congress has made a law abridging the freedom of speech.
This very topic is why I invited others to explain what the present state of the law in this area is. I doubt that Gitlow is still the level of protection required.
Virtually every public library contains a copy of Marx's Communist Manifesto. "Workers of the world, unite! You have nothing to lose but your chains!" is not a call to engage in collective bargaining. Prior restraint on speech is very rare.
I actually saw a man yell "Fire" in a crowded theater which was not on fire, and he was not jailed. It was Paul Newman in the movie "Torn Curtain". The speech itself is entirely protected and only negligent or criminal attempts to do bodily harm are outlawed.
If you know, please describe more recent case law on this matter.
It is certainly not the case that government has unlimited power to prevent its own destruction. Such a concept would allow violation of every restriction on government which could be written. Given that there are limits, then one ought to look to the written limitations to understand what those limits are. Our Founders chose "Congress shall make no law ...", not "Congress shall make no law except those which prohibit people from encouraging others to overthrow the government".
The laws concerning "conspiracy" are very close to abridgements of free speech. I believe that there is a requirement that at least one alleged conspirator commit some act in furtherance of the conspiracy in order to apply the law. There are then, do doubt, requirements for tying the other alleged conspirators to an intention to commit that act.