Here's an interesting Niebuhr quote I found in The Nature and Destiny of Man. This is a move to relativize us not a call to find some other absolute; not a common but needed function of religion.
Moral pride is revealed in all self righteous judgments in which the other is condemned because he fails to conform to the arbitrary standards of the self. Since the self judges itself by its own standards it finds itself good.
It judges others by its own standards and finds them evil, when their standards fail to conform to its own. This is the secret of the relationship between cruelty and self righteousness. When the self mistaks its standards for God's standards it is naturally inclinced to attribute the essence of evil to non conformists.
The character of moral pride is described in the words of St.Paul: "They have the zeal of God, but not according to knowledge. For being ignorant of God's righteouesness and going about to establish their own righteousness they have not submitted themselves onto the righteousness of God."
Moral pride is the pretension of finite man that his highly conditioned virtue is the final righteousness and that his relative moral standards are absolute. Moral pride thus makes virtue the very vehicle of sin, a fact which explains why the New Testament is so critical of the righteous in comparison with sinners.
The final proof that man no longer knows God is that he does not know his own sin. The sinner who justifies himself does not know God as judge and does not need God as Saviour. It involves us in the greater guilt. It is responsible for our most serious cruelties, injustices and defamations against our fellowman.