I can't remember where I heard this, but someone once said that defending a position by citing free speech is sort of the ultimate concession; you're saying that the most compelling thing you can say for your position is that it's not literally illegal to express.
A frustratingly obtuse comment, pretending that there's a rational discussion going on, with compelling arguments being made on both sides, evidence presented, rebuttals and refutations made, and so on. All quite civilized and liberal, a vibrant marketplace of contending ideas and visions.
That is not what's going on, not what's under discussion in recent "free speech" debates, and it's difficult to believe that Munroe is so oblivious.
The "argument" from the ilk Munroe is defending is, at bottom, "shut up". I.e., it's not an "argument" at all, it's a strenuous effort to squelch and delegitimize certain arguments.
Can Munroe really think that the blacklisters, the book-burners, the thought police, etc., act that way because they have the stronger argument?