From Christopher Lasch, The Revolt of the Elites and the Betrayal of Democracy (1996):
Both left-and right-wing ideologies, in any case, are now so rigid that new ideas make little impression on their adherents. The faithful, having sealed themselves off from arguments and events that might call their own convictions into question, no longer attempt to engage their adversaries in debate. Their reading consists for the most part of works written from a point of view identical with their own. Instead of engaging unfamiliar arguments, they are content to classify them as either orthodox or heretical. The exposure of ideological deviation, on both sides, absorbs energies that might better be invested in self-criticism, the waning capacity for which is the surest sign of a moribund intellectual tradition.