I know this is how people in the 80s and 90 imagined the future and a lot of concepts were probably too far fetched for them.
BUT... why arent they using drones to explore planets? why are there not more drone-spaceships? why does enterprise need a crew to begin with? Why is there so little automation? Why so few uses of AI in general?
I am saying this as a star trek the next generation person. I'd also expect them to have full video and sensory streams of any surface mission teams.
That's a totally insane explanation, though. Lots of people are on the ship at all times who aren't members of the crew, and that's before you even consider things like hostile boarding parties.
Most of the civilians present on the Enterprise fall into one of three categories:
A non-Starfleet staff member, relative, or passenger, who would already know and respect etiquette regarding ship's comms.
A non-hostile foreign diplomat, envoy, or similar passenger, who doesn't want to potentially cause a diplomatic incident by being rude.
I also recall lots of times where civilians used ship's comms for various purposes, but it was to contact the person directly attending to them, or a friend/relative, not the ship's captain. (It's been years since my last rewatch though so I could be wrong here...)
As for hostile parties, IIRC it's implied that the computer locks them out automatically, and in emergencies the captain can lock down the entire ship, which is how Data hijacked the Enterprise when he went rogue, and why it was such a big deal.