“Religion will always leaven the idea of justice with the ideal of love. It will prevent the idea of justice, which is a politico-ethical ideal, from becoming a purely political one, with the ethical element washed out.” (Moral Man & Immoral Society, p. 80-81)
Niebuhr, a self-proclaimed liberal, nailed it. Without the leaven of religion, societal justice is void of ethics. A very conservative view, wouldn’t you say?