Vulnerability of Space Settlements to Attacks

You're right that, just because of hazards and dangers from attacks, a space settlement doesn't have to be organized along paramilitary lines for security. But I've encountered many arguments for regimented, strictly monitored and controlled space societies, using the hostile space environment and the vulnerability of a space habitat as justification.
That is the common perception, but I think it's based more on what we see in science fiction movies and TV shows than what we might reasonably expect in reality. In SF, the danger of explosive decompression is ever-present. Air flow from a hull breach can pick up a full-grown man, pull him tens of feet through the air, and then suck him out a hole the size of a bowling ball. And the "life support system" is some electronic box with blinky lights. A cessation of operation for even a few minutes results in the heroes gasping and panting for life.
But that's all because that's what serves the writer's needs for high drama. O'Neill calculated that the dangers of a hull breach are much more modest than what SF would lead us to think. Airflow though a hull breach may be supersonic at the breach itself, but quite gentle just a few feet away. And the "life support system" in an orbital habitat would be every green plant growing in sunshine. Some of the smaller, shielded models will require active cooling, but this is done with nothing more high tech than electric fans circulating air though passive radiators. And there can be many dozens of fans and independent power systems.
If life in a space habitat were to become strictly regimented, one could not honestly use "the ever-present dangers of space" as a justification for it.
I sooner expect that life here on Earth will become increasingly regimented as time goes on.