Earlier quoted context omitted.
That's not the case; if speech is considered an action like any other, it can be regulated like any other action. The implication is not that actions are forbidden unless they are specifically allowed. You aren't specifically allowed to eat fries or post comments on HN - yet you do so anyway. And you would, rightly, resist a law which says you can't, just as you'd resist a law which contravenes a constitutional right…
OK you finally confused me enough that I had to click through your link and read. I was somewhat disconcerted that the first thing I read was "please don't distribute this link publicly" (was that ironic?). Later on when discussing the crux of this thread (is there a significant difference between speech and other physical actions?), the author dropped an "[as] I’ve argued in previous work..." on us. There is referen…
Regarding the bulwark against authoritarianism, this is already hinted to - being particularly hazardous about policing speech doesn't make so much sense when we already legislate on many other issues which seem to have bigger effects - such as food safety regulation, or the law of murder, or laws against literal genocide. I feel similar to Schauer here, but I'm uncomfortable about taking the plunge and sticking to the unjustified status quo which already seems to produce unfavorable results without much going for it. Even under a system with no free speech law, we'd have no reason to think political speech would necessarily be repressed but good reason to think that various reasoned arguments against hate speech and pornography would be entertained - to me that's a good thing.