When did "liberals" stop believing in Free Speech?

When I was in law school in the early 1980s, free speech was the constitutional value that trumped all others. The idea of limiting free speech so as to not print "How to build a nuclear bomb" was considered anathema. No one was concerned about offending people or making them feel unsafe by flag burning.

But there was a current that was sure that they knew where to draw a brand new line.  One of my professors at UCLA wrote a book in the 1980s about how First Amendment protections should not be extended to Nazis.

Next thing we know is that suddenly we find that "your speech is harmful, but our speech is just lovely."

Tucker Carlson captures this prevailing wisdom in his interview with a college professor who seems like a caricature of her profession in being unwilling to actually say where she would draw the line, lest she appear too much like the fascist she is.