There is such a law, the Smith Act: 18 USC 2385 (Advocating overthrow of Government), which says in part
Whoever knowingly or willfully advocates, abets, advises, or teaches
the duty, necessity, desirability, or propriety of overthrowing or
destroying the government of the United States or the government of
any State, Territory, District or Possession thereof, or the
government of any political subdivision therein, by force or violence,
or by the assassination of any officer of any such government...
shall be punished. My reading of the offending text is that it states the desirability of an action which some people probably think would result in the overthrow of the US government by force, but does not directly commit the offending act.
In Yates v. United States, 354 U.S. 298, the Supreme Court ruled that
The Smith Act does not prohibit advocacy and teaching of forcible
overthrow of the Government as an abstract principle, divorced from
any effort to instigate action to that end
Although the court did not rule that the act was unconstitutional, it limited its application to the point of virtual unenforcibility.
Speech can only be limited when it presents a "clear and present danger". As ruled in Brandenburg v. Ohio 395 U.S. 444, speech cannot be restricted
except where such advocacy is directed to inciting or producing
imminent lawless action and is likely to incite or produce such action