Most societies are confusing to an outsider, but in order to function they must make sense from their own perspective. Thus most societies follow certain basic rules; they protect their members (or, arguably, some of their members) and create an environment where they can fulfil their function or pursue their wishes. There is usually some form of organisational structure in place to regulate activity and prevent excessive internal conflict.
However, societies do break down, or become skewed by internal or external factors to the point where they cannot survive in the long term. There is nothing to prevent the referee from coming up with a very odd, perhaps even incomprehensible, social structure. However, there needs to be a reason for whatever set up exists, even if it is never revealed to the players.
Written by fan-favourite M J Dougherty, Societies and Settlements is an invaluable addition to the Referee's Aid series, exploring the different governments, cities and other settlements of the galaxy and discovering how they can be used to influence campaigns.