One of the problems with living in a society with no shared moral order is that we have no way to settle arguments. We have no objective standard by which to determine that one view is right and another view is wrong. So public arguments just go on indefinitely, at greater levels of indignation and polarization. People use self-righteous words to try to get their way, but instead of engaging in moral argument, what they’re really doing is using the language of morality to enforce their own preferences.
But this happened in the older societies as well. Earlier, Brooks even says that the Enlightenment came about because of the endless mass killing.