Is the price of freedom, says the saying. The same is evidently true of an egalitarian societies. Hunter gatherer bands are more or less universally egalitarian, but this egalitarian structure is not maintained without a struggle. Stronger, smarter, or otherwise advantaged individuals are continually attempting to gain dominance over the others. This tendency is balanced by the ability of the weaker members to form coalitions and deploy the weapons of social coercion against the would be dictator: gossip, other social sanctions, and if truly necessary, banishment or homicide. The intellectual tools we have developed seem to work quite well in suppressing dictators at the level of the band or small tribe.
They don't seem to have been adequate once people became settled agriculturalists and started living in much larger groups. That development set the world on a path of extreme hierarchy and despotism which has dominated our history for the past several thousand years. If, as Christopher Boehm hypothesizes, our long hunter gatherer stage promoted the evolution of behaviors suitable for egalitarian societies, it's hardly implausible that the last 5000 or so have undermined those, possibly at both the cultural and biological level.
Sporadic reassertions of egalitarianism have popped up throughout history, but they have usually been temporary. The last several hundred years have been the largest such fluctuation in history. Can we preserve it?
Defenders of Aristocracy have mostly crawled under rocks these days, but the rise of the modern plutocracy has energized its defenders. Prominent economist Greg Mankiw's Defending the One Percent is a very contemporary example, but hardly isolated, since the virtually complete domination of the media by a few zillionaires gives them broad access to every organ of propaganda. Modern defenders of aristocracy come in a few flavors: psuedo-Nietschean Ayn Rander's, Libertarians, and old-fashioned Romney type robber barrons, to name a few.
One lesson from the study of the evolution of human behavior, I think, is that an egalitarian society is fragile, and that the old weapons of the stone age may no longer be adequate for its maintenance.