Epsilon minus - addressing someone by his/her first name IS correct. After all, they do call me by my first name, so why should I call them Captain/Sir/Madam? That would be demeaning to myself. When they don't know me and I get on the flight deck, the first thing they do is to shake hands with me and say "Hi, my name is John" or something to that effect. I guess that means I can then call them by that first name.
If my colleagues were judges or doctors, I would indeed call them by their first name. I know the medical profession well enough from the inside to know that this is what they do. This is the 21st Century guys, and I'm NOT into the British class society thing. Full stop. Never had any complaints.
Respect is something that is earned, not automatic.
Cheers