Earlier quoted context omitted.
If you don't believe in censoring communications between a willing-speaker & willing-listener, anything they do has a 100% false-positive rate.
If only Facebook, Twitter, and YouTube were completely full of willing listeners for hate speech, then that might be applicable. Hate groups aren't sending private forum messages to each other, they're broadcasting Even John Stuart Mill, a founding philosopher of free speech, postulated that speech needs to be curtailed when the expression harms others.
The classical line has been at incitement. It understands that humans are prone to irrationality in the heat of anger. But outside of that it is understood that some harm may be necessary for justice or other ideals to be served. Speech is the mechanism we use to weigh the costs of our actions.