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Well-known
I think you are dead wrong on this. Friends call each other by first name. In academia and even in a professional environment here in the US, everyone is on first name basis, nobody would every say "Mr", "Dr" or "Professor", that's a last century mindset.
When I was working on my Masters Degree in Philosophy after I retired, I always addressed my professors as Professor [last name] even though they were much younger than I was. It is a sign of respect.
When I visit my physician for a checkup or am treated by my physicians in the hospital, I always address them as Dr. [last name], even though I have known them for years. It is a sign of respect.
I guess I just have a last century mindset.
So speak for yourself from your limited experience, and not for everyone here in the U.S.