"As long as people are polite when addressing other people, what's the problem ? Rather than have a list of titles to use and trying to figure out which one suits the occasion, what's wrong with a polite ' hello ' ?"
Nothing wrong with that or being polite at all. Nothing wrong with "everybody" (albeit a bit unprofessional in a formal setting). What starts out completely innocuous will become a C-16 or similar and that's my gripe. You can call me a snowflake for pointing out the deviants' softly-softly approach but It's not getting past me.