“he regarded it with the feelings due not to a mere mental delusion, but to a great moral evil. He looked upon it as the greatest enemy of morality: first, by setting up factitious excellencies, -- belief in creeds, devotional feelings, and ceremonies, not connected with the good of human kind, -- and causing these to be accepted as substitutes for genuine virtues: but above all, by radically vitiating the standard of morals; making it consist in doing the will of a being, on whom it lavishes indeed all the phrases of adulation, but whom in sober truth it depicts as eminently hateful.”

Matterhorn: A Novel of the Vietnam War, Ch. 19 (2010).
Context: He thought of the jungle, already regrowing around him to cover the scars they had created. He thought of the tiger, killing to eat. Was that evil? And ants? They killed. No, the jungle wasn't evil. It was indifferent. So, too, was the world. Evil, then, must be the negation of something man had added to the world. Ultimately, it was caring about something that made the world liable to evil. Caring. And then the caring gets torn asunder. Everybody dies, but not everybody cares.It occurred to Mellas that he could create the possibility of good or evil through caring. He could nullify the indifferent world. But in so doing he opened himself up to the pain of watching it get blown away. His killing that day would not have been evil if the dead soldiers hadn't been loved by mothers, sisters, friends, wives. Mellas understood that in destroying the fabric that linked those people, he had participated in evil, but this evil had hurt him as well. He also understood that his participation in evil, was a result of being human. Being human was the best he could do. Without man there would be no evil. But there was also no good, nothing moral built over the world of fact. Humans were responsible for it all. He laughed at the cosmic joke, but he felt heartsick.

Source: On Liberty

Paris Review interview (1958)

"The Reasons for My Involvement in the Peace Movement" (1972) http://www.shalomctr.org/node/61; later included in Moral Grandeur and Spiritual Audacity (1996)
Context: There is immense silent agony in the world, and the task of man is to be a voice for the plundered poor, to prevent the desecration of the soul and the violation of our dream of honesty.
The more deeply immersed I became in the thinking of the prophets, the more powerfully it became clear to me what the lives of the Prophets sought to convey: that morally speaking, there is no limit to the concern one must feel for the suffering of human beings, that indifference to evil is worse than evil itself, that in a free society, some are guilty, but all are responsible.

Source: Self-Help; with Illustrations of Character and Conduct (1859), Ch. I : Self-Help — National and Individual

Source: Morals and Dogma of the Ancient and Accepted Scottish Rite of Freemasonry (1871), Ch. XXII : Grand Master Architect, p. 192

Source: Dorothy Thompson’s Political Guide: A Study of American Liberalism and its Relationship to Modern Totalitarian States (1938), p. 78