When did the left turn against free speech?

One of the commenters declares that my "assertion that 'the best test of the truth is its ability to get accepted in the marketplace of ideas' was probably the most offensive part of her argument." When questioned about whether I really said that, he comes back with:

She cited a Justice whose name I haven't retained, as in: "As Justice X says, ..." followed by the verbatim passage I quoted.

She cited a Justice whose name I haven't retained.... Oh, for the love of God, why doesn't every educated person in America know the name of the Supreme Court Justice who said that... or at the very least know that it's embarrassing not to know? As if I'd thrown out some abstruse legalistic peculiarity!

And that was part of an argument by the commenter — echoing Bob Wright — that free speech is too dangerous because it might be false and it might inspire bad people to act out in terrible ways.

Remember when lefties were all about free speech? When did that change? Why did that change? Perhaps the answer is: Free speech was only ever a means to an end. When they got their free speech, made their arguments, and failed to win over the American people, and when in fact the speech from their opponents seemed too successful, they switched to the repression of speech, because the end was never freedom.