My comment was always (for the UK market):
"If it is mandatory to wear a seatbelt when travelling in a car up to 70 mph, and I am sure you have seen the adverts about it... why on earth would you not want to wear one when you are travelling 550 mph?"
Never had an issue with it after that........
Can genuinely understand though why people question it when they see us walking around the aircraft when seat belt sign is on...
Is all about talking to people as adults and trying to explain the reasons behind it, be it seat belts, no smoking signs, alcohol..
As for armrests, agree with all above and usually have to explain it to numerous people, once is understood, again, never had an issue....
Safe flying all . . . . . . . . .