Well, they’re all basically locked in a submarine, but way worse. You’re in a sealed box hurtling through space. You need a doctor on board, and you need a counselor on board. If you don’t want both of them to go completely insane, both of them also need friends and social interaction.
While I agree that Starfleet levels of general fraternization are a lot looser than in modern military, I also think it’s just kind of something you learn to live with when you serve on a ship.
I think we’re, at least, led to believe that Starfleet officers are better adjusted than your average early 21st century human. For example, we don’t see a lot of gossip behind Riker’s back about how he gets around, but you very probably would today.
It may still not be ideal, but I think it would be less problematic than it would be for us.
