What is the nature of society? Why do people get along? Why do they not get along?
Let's go meta:
These questions must be very very old and must have been asked over and over again since the dawn of human civilization, so one would expect a lot to be known about the answers. Over the generations, wrong answers should have gotten weeded out. We should be left with a very accurate, very detailed consensus descriptive model of how humans behave within arbitrary societies, and why they do. (Not a normative model of how humans should behave, of which there are plenty.) Given how useful such a model would be, we would expect the model to be broadly known, common knowledge.
No such model exists. Why not?
- The American experiment, an ostensibly classless, atheistic, melting pot society within which people marry for love, is so different from anything done before in written European history that there is no useful previous research.
- The answers have been discovered many times already, but laying bare human behavior in its entirety is so disgusting and vile that censorship mechanisms cause the information never to be published, then lost.
- The answers are known, but because such a model can be powerfully used to deceive and manipulate, the answers are concealed and closely guarded by those who have it for their selfish ends.
- Human behavior is so complex that even after hundreds or thousands of years of effort, we are not even close to a good model. (For example, game theory is but a 20th century discovery, and refinements of Nash equilibria are still an active area of research.)
All these hypotheses seem unlikely.