A hive mind? A society so thoroughly integrated, even on a biological level that individual existence is not only impossible, but is also inconceivable. Your very existence outside the hive is a wrong. All you are is anathema.
If you want to go dark, use the "people as parts" idea from the Dr. Who episode Girl In The Fireplace to explain tech level anomalies.
If you want to go really dark, consider Honeypot ants or the "humans as batteries" idea from the Matrix movies.
Red Zone the heck out of the place and the Scout/Naval bases are there as wardens/observers/first contact hubs.
For a real hoot, put two or three of these worlds in proximity to each other and you've got a built-in conundrum of how they got there.