In "Picking What We Like From Niebuhr" Barton Swaim reviews the documentary and observes that people across the ideological and/or theological spectrum claim admiration for him. From that review:
.... I watched the documentary's treatment of Niebuhr's best and most famous work, Moral Man and Immoral Society. ....The book's basic idea is this: While people are capable of "moral" or altruistic behavior as individuals, they become cold and cruel, even vicious, when they act as collectives. Men and women are able to act morally in some circumstances; governments and nations basically are not. Political ideologies built on the idea that man can create a perfectly just society by means of collective coercion are therefore doomed to failure. "There are definite limits of moral goodwill and social intelligence," he writes, "beyond which even the most vital religion and the most astute educational programme will not carry a social group, whatever may be possible for individuals in an intimate society."
The best check on group egoism, Niebuhr contends, is not coercion by a technocratic elite but the ordered conflict of democracy. What is lacking in the worldview of Thomas Dewey and other progressives, he writes,
is an understanding of the brutal character of the behavior of all human collectives, and the power of self-interest and collective egoism in all intergroup relations. Failure to recognize the stubborn resistance of group egoism to all moral and inclusive social objectives inevitably involves them in unrealistic and confused political thought. They regard social conflict either as an impossible method of achieving morally approved ends or as a momentary expedient which a more perfect education or a purer religion will make unnecessary. They do not see that the limitations of the human imagination, the consequent persistence of irrational egoism, particularly in group behavior, make social conflict an inevitability in human history, probably to its very end.That is a powerful argument. Its implications, whatever one's philosophical allegiances, are bewildering. It's applicable to the utopian ideologies of communism and Social Gospel theory with their wild optimism about human nature, modern progressivism and "compassionate conservatism" with their faith in bureaucratic benevolence, and even the new Trumpian nationalism with its confidence in the restorative power of unity and patriotism. ....
.... Liberal Protestant theologians in the first third of the twentieth century no longer took the doctrine of sin seriously, believing man to be perfectible. Niebuhr forcefully told them they were wrong. He brought an "Augustinian sensibility" to the debate—which is a radical theologian's fancy way of saying Niebuhr insisted on the inescapable reality of sin in human life. .... [more]