I've always believed and agreed with this. In a fragmented society, people will form sub-collectives with their own personal goals and interests, ones that often directly compete against that of other groups. This inevitably results in jockeying for power, where politics/elections/whatever boil down to interest groups lobbying and buying off as many politicians as possible in order to benefit their own kind the most. The idea that you can simultaneously preserve the major differences between races and cultures (diversity is our strength! Muh taco stands!), and also have everyone work together and cooperate fully, is insane.