Source: The Animal Welfare Movement and the Foundations of Ethics, p. 89
“… 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.”
"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.
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Abraham Joshua Heschel 130
Polish-American Conservative Judaism Rabbi 1907–1972Related quotes

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.

"Donald Trump: Playboy interview" , Playboy magazine, March 1990. http://www.popeater.com/2009/09/30/donald-trump-insults/
Helmsley retorted "I can't wait to read Trump's new book, especially chapter eleven!". At the time, Trump's casino holdings were being reorganized to avoid bankruptcy.
"Leona Helmsley: Playboy interview" , Playboy magazine, November 1990. http://www.glennplaskin.com/leona.pdf
1990s

River out of Eden (1995)

Attributed to Bonhoeffer on the Internet, and supposedly from Bonhoeffer: Pastor, Martyr, Prophet, Spy http://books.google.com/books?id=aG0q3X8TVpsC&pg=PA486#v=onepage (2010) by Eric Metaxas; however, there is no actual reference in that book. However, in advertising the book Metaxas does state on his site that the quote is from Bonhoeffer. http://ericmetaxas.com/books/bonhoeffer-pastor-martyr-prophet-spy/ First attributed to Bonhoeffer in Explorations 12:1 (1998), p. 3, as referenced by James Cone (2004) Theology's Great Sin: Silence in the Face of White Supremacy, Black Theology, 2:2, 139-152, footnote 1 http://dx.doi.org/10.1558/blth.2.2.139.36027
Compare "Not to Act, is to Act!" by Francis W. McPeek http://www.ergo-sum.net/pics/McPeek.jpg, The Missionary Herald at Home and Abroad, v.141-142 (1945-1946), "Missionary herald, 1945 - Congregational churches," pp.34-35 (We must realize that church inaction is a form of political action, and it is altogether negative. “Not to act, is to act.”)
Misattributed

p, 125
Spiritualism and the Christian Faith (1918)

Part 1, Section 1
A Treatise of Human Nature (1739-40), Book 3: Of morals
Context: Morality is a subject that interests us above all others: We fancy the peace of society to be at stake in every decision concerning it; and 'tis evident, that this concern must make our speculations appear more real and solid, than where the subject is, in a great measure, indifferent to us. What affects us, we conclude can never be a chimera; and as our passion is engag'd on the one side or the other, we naturally think that the question lies within human comprehension; which, in other cases of this nature, we are apt to entertain some doubt of. Without this advantage I never should have ventur'd upon a third volume of such abstruse philosophy, in an age, wherein the greatest part of men seem agreed to convert reading into an amusement, and to reject every thing that requires any considerable degree of attention to be comprehended.

“Fear of evil is greater than the evil itself.”
Sono maggiori li spaventi ch'e mali.
Act III, scene xi
The Mandrake (1524)