Our listing has extra fees if there are more than 2 people booking and there have been a number of instances where guests would sneak in extra people.
We got a security camera for one of our listings recently. It's an attached suite with a private entrance. The camera is installed outside and it's disclosed with a check box toggled in Airbnb's listing settings.
Being a private person myself, I would not put a camera inside spaces meant private for guests. In these times, I'm even a bit wary on adding a CO alarm because guests might think it's a spy camera.
Obviously, not everyone has the same standards. The host described in the post is quite rude. I wouldn't communicate that way with a guest. Hopefully, Airbnb will reopen the case given the attention it has received.