I became aware of this censorship in academia by sheer accident in 1973. I was heading towards Key West in my VW camping bus, and on the way I stopped by the University of Florida where I came across a news item that a philosopher was in court fighting his firing. I had forgotten his name, but I do remember that he was a Marxist who spoke his mind in an unvarnished fashion. I stayed to listen to the testimony of the president and others. But I did not stay to find out the outcome of these hearings. But searching the internet, I have found out that the philosopher was Kenneth A. Megill, who appealed a denial of tenure by President Stephen C. O’Connell. I found the following court ruling: Dr. Kenneth A. MEGILL, Plaintiff-Appellant, v. BOARD OF REGENTS OF the STATE OF FLORIDA et al., Defendants-Appellees.
I remember other such cases. The one that sticks in my mind was the dismissal of Saul Kripke. At the time I heard of this, I was — let us say — bewildered: Saul Kripke??? Again, scouring the internet, I found this informative piece: Israel Shenker, “Rockefeller University Hit by Storm Over Tenure,” Sept. 26, 1976. Reading the piece, I discover that a whole group of other eminent philosophers had to find employment elsewhere.
Other cases of professors being fired — the euphemism is non-reappointment — or denied tenure which come to mind, are that of Howard Zinn who was dismissed from Spelman College in 1963 for supporting student protests as an act of insubordination.
The case of Norman Finkelstein was especially disconcerting to me, and I wrote a big analytical piece about it: Norman Finkelstein, DePaul, and U.S. Academia: Reductio Ad Absurdum of Centralized Universities, July 23, 2007.
There is a short clip of me here, identified as Philosophy Teacher, Wright College, Chicago, offering my two bits :
Professor Finkelstein’s DePaul Farwell, Sept. 5. 2007:
Below is a full-documentary about Norman Finkelstein:
American Radical: The trials of Norman Finkelstein 
Ward Churchill, a tenured professor, was fired from the University of Colorado in 2007 on alleged plagiarism charges but really for claiming in an article and a book that the 9/11/2001 attack against the World Trade Center was — to use Chalmers Johnson’s CIA word — a “blowback” for the U.S. policies in the Middle East. Churchill took the wrongfull dismissal case to a court, and won; but was not reinstated. The controversial article was “Some People Push Back: On the Justice of Roosting Chickens,”, Sept. 12, 2001, and the book was On the Justice of Roosting Chickens: Reflections on the Consequences of U.S. Imperial Arrogance and Criminality, 2003.
Below is Megyn Kelly’s commentary and interview with Ward Churchill in 2014.
There is also the case of David Graeber whose contract was not renewed at Yale. Below is a link to an interview with Graeber about this affair.
Joshua Frank, “David Graeber is Gone: Revisiting His Wrongful Termination from Yale,” Counterpunch, September 4, 2020.
The whole issue of censorship in America has recently been put on film: No Safe Spaces