Considering this is repeated a couple times by the author, it seems they are talking about a general statement and not a narrow circumstance, even if they're using a specific example. It's important to point out that the statement above is not universally true, or if it is, then our laws are immoral.
"Again, those are legal principles that have been enshrined in law for a long time."
“When we do become offended, as we all will, we must settle for responding with criticism or contempt, and stop short of demanding that the offender be punished or required to make restitution,”
It seems to me that restitution and punishment would include those leveled by the legal system. Simply because something has be law for a long time does not make it off limits to discussion, especially if it's application/interpretation has changed over that time.
When it comes to public universities, there is a legitimate question, since a publicly funded university may be considered a state actor. But when it comes to private services like social media where it seem most of the controversy lies, they're free to set any rules they want. And unsurprisingly, their terms of service generally give them broad discretion on who they let use their service.