We are talking about freedom of choice.
In the future, space colonies will number in the thousands if not millions. I imagine they'll be populated by everything from fascistic hippies to pot smoking cyborgs, and everything in between. Any and every type of society will exist for you to choose from. Some will be closed gated communities, while others will be totally open to everyone. They say good fences make good neighbors. If that's true, then a few million miles of hard vacuum should be one hell of a fence.