Thanks jetset lady. You said exactly what I would have said if I'd had your knowledge, or to put it another way, what I imagine I would have said if I were CC. In fact I did, many years ago, when I worked for a UK charter carrier, work as supernumerary (I almost couldn't even spell that) CC on charters to East Africa.
I think my main point would have been your first one, and even now I get very irritated when the CC or flight deck request that passenger keep their seat belts fasten in case of turbulence, and half the pax are all gung-ho and don't bother.