“Doubtless there are times when controversy becomes a necessary evil. But let us remember that it is an evil.”

Source: Dominion: The Power of Man, the Suffering of Animals, and the Call to Mercy

Source: Losing My Virginity: How I've Survived, Had Fun, and Made a Fortune Doing Business My Way

51
The Zürau Aphorisms (1917 - 1918)

Churchill By Himself: The Definitive Collections of Quotations, ed. Richard Langworth, 2008, p. 424, (1907, 12 February)
Early career years (1898–1929)

Unidentified fragment 651.

King's often repeated expression that "The arc of the moral universe is long, but it bends towards justice" was his own succinct summation of sentiments echoing those of Theodore Parker, who, in "Of Justice and the Conscience" (1853) asserted: "I do not pretend to understand the moral universe; the arc is a long one, my eye reaches but little ways; I cannot calculate the curve and complete the figure by the experience of sight; I can divine it by conscience. And from what I see I am sure it bends towards justice."
1960s, Where Do We Go from Here: Chaos or Community? (1967)
Context: I must confess, my friends, the road ahead will not always be smooth. There will be still rocky places of frustration and meandering points of bewilderment. There will be inevitable setbacks here and there. There will be those moments when the buoyancy of hope will be transformed into the fatigue of despair. Our dreams will sometimes be shattered and our ethereal hopes blasted. We may again with tear-drenched eyes have to stand before the bier of some courageous civil rights worker whose life will be snuffed out by the dastardly acts of bloodthirsty mobs. Difficult and painful as it is, we must walk on in the days ahead with an audacious faith in the future. … When our days become dreary with low-hovering clouds of despair, and when our nights become darker than a thousand midnights, let us remember that there is a creative force in this universe, working to pull down the gigantic mountains of evil, a power that is able to make a way out of no way and transform dark yesterdays into bright tomorrows. Let us realize the arc of the moral universe is long but it bends toward justice.

"Self Esteem" (31 May 2007) http://www.youtube.com/watch?v=RNBgCKvjrb4
Context: I've been asked by a lot of new YouTube people or other singers — all kinds of professions, frankly, as to whether I feel very successful and very loved now that I've got bup-up-up-up subscribers and however many nice comments and sweetness, and I really, really do! I was thinking going into this that the odds were against me — you're online, there's this anonymity, people are mean sometimes, and still considering all that, it's overwhelming the sweetness and the affection that I am getting — I'm every day impressed by this — every day! And there are a lot of horrible, horrible people on here, just like there is in the rest of the world. But remember, "don't be overcome with evil — overcome evil with good."

Source: The Magic Mountain (1924), Ch. 6, section, A Good Soldier as translated by Woods (1996), p. 506