Fair enough Flaps Forty. All I was getting at is that it is inevitable that passengers will get out of their seats to use the facilities if the FSB sign has been left on for length periods of time (over an hour) in smooth conditions with no information from the flight deck. When I deadhead I would say that the majority of the time flight attendants become complacent during these situations and do not enforce the fasten seatbelt protocol. The passengers have a valid concern and complaint when it comes to the FSB sign protocol at many major airlines. Unless actually experiencing or truly expecting moderate turbulence it is unacceptable to keep everyone seated for hours at a time.
However, when passengers are seated I think they should be required by law to keep their seatbelts fastened.