It's simple really. Nothing is wrong with it. Society, like anything else created by our social behavior, is following human evolution ever since we started living together within small and functionally organized communities. In the beginning there was a simple need for this - it was impossible for just one man to hunt down one, for example, mammoth or to defend a family from the herd of prehistoric saber-tooth tigers and the only solution was to get together and organize a little for the mutual benefit. Not to mention everlasting need for prolonging the species which also required, sort of, well, socializing with a member of opposite gender. Mammoth hunt and prehistoric society* We can only wish that things are as simple as it was millenniums before. If we disregard the fact that socializing in order to save the species didn't change much from the times where humans shared the habitat with mammoths, all other aspects of one human society, due to the thousands of years