Yes I start my PA with Captain "..."
I am in command of the aeroplane and am not inviting any passenger to address me by my first name. There are standards which I intend to maintain.
Ask any of the Nigels if they had any problem with calling their superiors 'sir'.
This is an airline; there is no income without aeroplanes moving from A to B and that means a Captain and that means we are the most important people in this business. Think of the EK clinic; the Doctors there are religiously called by Dr "first name". We are called by our first name only but this an airline not a hospital. There is no respect for us and I for one will insist on it. To do otherwise is a slight on our profession/job/trade.