> I haven't been in a bar where the patrons were told they couldn't discuss quack medicine.

That's over specific.

All bars (even the worst ones I could find) usually have unspoken rules about what can be discussed, until you start to talk about those subjects (eg drug dealing, weapons dealing, planned violence, etc) openly. Of course you can't effectively restrict communication between individuals, but that's also not the issue.

Maybe. I was in a Bait and Tackle shop yesterday that had a sign on the door warning of a $100 fine for speaking the word "coronavirus" inside.