I figured with the focus on Reinhold Niebuhr, it would be good to quote his brother, H. Richard who raises an unsettling idea:
A dark prospect opens before us as we reflect on the meaning of Jesus' question "When the Son of man comes will he find faith on earth?" (Luke 18:8) He may have meant, "Will he find belief or trust in God" But he may have also meant, "Will he find any faithfulness among men?"
The experiences of the 20th century have brought into view the abyss of faithlessness into which men can fall. We see this possibility that human history will come to its end neither in a brotherhood of man nor in universal death under the blows of natural or man made catastrophe:
But in the gangrenous corruption of a social life in which every promise, contract, treat and "word of honor" is given and accepted in deception and distrust. If men no longer have faith in each other, can they exist as men?