… is from page 27 of Lionel Trilling’s Winter 1948 Kenyon Review essay titled “Manners, Morals, and the Novel“; I learned of this quotation – and of the essay in which it appears – from reading the late Gertrude Himmelfarb’s 1994 volume, On Looking Into the Abyss, where she herself uses this quotation on page x:
Some paradox of our natures leads us, when once we have made our fellowmen the objects of our enlightened interest to go on to make them the objects of our pity, then of our wisdom, ultimately of our coercion. It is to prevent this corruption, the most ironic and tragic that man knows, that we stand in need of the moral realism which is the product of the free play of the moral imagination.