Government can and does restain speach. It issues gag orders, classifies information, places and enforces injunctions, and facilitates private bounds on speech through patent, trademark, and copyright law, trade secrets, and recognition and enforcement of nondisclosure and nondisparagement contracts. Even forms of observation may be limited under espionage or treason laws. Limits are placed on incitement, inflammatory speech, pornography, indecency, and "fighting words".

Freedom of speech, as with other legal and civil rights, is an ideal, not an absolute. It has evolved tremendously within the US, arriving at a form we'd recognise currently only in the 1950s and 60s, about 60 years ago. The famous "shouting 'fire' in a crowded theatre" objection was raised in a case (Schenck) in free speech was found not to apply to anti-draft advocates during WWI, barely over a century ago.

And the US Supreme Court's "marketplace of ideas" standard is similarly quite problematic, owing far more to free-market fundamentalist advocacy than some doctrine of prevailing truth.

Turns out it was always more a bit of pro-free-market-fundamentalism propaganda than a pro-truth notion.

See Jill Gordon, “John Stuart Mill and the ‘Marketplace of Ideas’"

https://philpapers.org/rec/GORJSM

Or Stanley Ingber, “The Marketplace of Ideas: A legitimizing myth”.

https://scholarship.law.duke.edu/cgi/viewcontent.cgi?article... (PDF).