I get your point, but ... > It would be akin to a city floating on Earth's open ocean. With all food, household items etc, and even construction materials prod

I get your point, but ... > It would be akin to a city floating on Earth's open ocean. With all food, household items etc, and even construction materials produced via extraction from the surrounding ocean. Akin in some senses, but let's not omit that another planet would be far, far more difficult. Humans do live on boats and islands in oceans; we can breathe the air, drink the water (if desalinated), eat the fish, swim, build boats from resources, etc.