After reading “The moon is a harsh mistress” I was wondering whether line marriages can be an alternative for the (welfare) state. As a person with some libertarian leanings (however, I am NOT a libertarian myself) I believe one should investigate whether there are plausible alternatives for the “state” and whether these alternative should be preferred above the state.
But I will first give a short impression of Heinlein’s concept of line marriage in The moon is a harsh mistress. In this novel the Moon is colonized by humans, the Lunar government is set up and run by the United Nations, while Lunar society is highly anarchistic. The primary purpose of the Lunar government is to ensure the delivery of grain to Earth, and the local population is mostly left on their own. All necessities of life are to be bought, even air.
In this harsh environment, it is not surprising that people are seeking cooperation. One of the forms described, and the only one actually discussed in detail, in The Moon is a harsh mistress, is the line marriage. In this kind of marriage multiple people are married together, and in the course of time new spouses are allowed to enter the line. In theory such marriage can survive for generations, even if the original spouses have been dead for centuries. Since the potential durability of a line, all wealth collected by it, will be kept together. The particular line described by Heinlein, is highly self-sustaining, they produce their own food and recycle their own water.
Since the bond between the spouses, of both sexes, is based on mutual affection the members are ensured of assistance whenever required. Younger spouses take up the care of the elderly, children have virtually no worries about being orphaned.
Personally I do not believe that the Moon is the proper place for human settlement. When the age of space colonization will seriously begin, space habitats would be build in the neighborhood of the Near Earth Objects. And these first space colonies will be the initiative of either corporations or governments, therefore the governance of those early space colonies will be rather bureaucratic. Only after a few decades, as predicted by O’Neill , some private individuals will start their own small space colonies.
In chapter 11 of The high frontier, O’Neill describes how five couples and their families leave their own space habitats and travel for months to the asteroid main belt. Instead of group of five separate families, we can easily imagine how a family of a line marriage travel to the Belt.
In the neighborhood of asteroid, especially the smaller ones, there will be enough resources for a group of people to survive for generations. Barter with other groups in the Asteroid Belt will enable a group to meet all their material needs. And since distances between several group is large, the development of large conflicts is unlikely and if one group get into to trouble with a neighboring group/tribe/clan they can move with all their belongings to somewhere else in our Solar System, space enough. Therefore such settlers will not have great need for establishing a powerful government. The only reason to do this is in case of an external threat, but this unlikely since due to both the self-sufficiency and large distances military operations are almost futile to begin with.
 The high frontier, chapter 11.