“We in Africa are always on the receiving end. We have had human slavery, political slavery, economic slavery and now religious slavery. We in the church are saying no. We are prepared to live by what God says, not what you say. Man shall not sleep with man, woman shall not sleep with woman.”

Speech to the Virginia Convention (1861)

Quoted by Courtlandt Palmer, president of the Nineteenth Century Club of New York, while introducing Robert G. Ingersoll as a speaker in a debate, "The Limitations of Toleration," at the Metropolitan Opera House, New York City (1888-05-08); from The Works of Robert G. Ingersoll (Dresden Publishing Company, 1902), vol. VII, p. 217

[Why It's Time to End Factory Farming, October 20, 2018, Quillette, https://quillette.com/2018/10/20/why-its-time-to-end-factory-farming/]

King quoted here John F. Kennedy who at the signing of a charter establishing the German Peace Corps in Bonn, West Germany (24 June 1963) remarked: Dante once said that the hottest places in hell are reserved for those who, in a period of moral crisis, maintain their neutrality.
According to Bartleby.com, Kennedy's remark may have been inspired by the passage from Dante Alighieri’s La Comedia Divina “Inferno,” canto 3, lines 35–42 (1972) passage as translated by Geoffrey L. Bickersteth: "by those disbodied wretches who were loth when living, to be either blamed or praised. [...] Fear to lose beauty caused the heavens to expel these caitiffs; nor, lest to the damned they theng ave cause to boast, receives them the deep hell." A more modern-sounding translation from the foregoing Dante’s Inferno passage was translataed 1971 by Mark Musa thus: “They are mixed with that repulsive choir of angels … undecided in neutrality. Heaven, to keep its beauty, cast them out, but even Hell itself would not receive them for fear the wicked there might glory over them.”
This is also often quoted slightly differently as: "The hottest place in Hell is reserved for those who remain neutral in times of great moral conflict"
1960s, Why I Am Opposed to the War in Vietnam (1967)
Context: I see this war as an unjust, evil, and futile war. I preach to you today on the war in Vietnam because my conscience leaves me with no other choice. The time has come for America to hear the truth about this tragic war. In international conflicts, the truth is hard to come by because most nations are deceived about themselves. Rationalizations and the incessant search for scapegoats are the psychological cataracts that blind us to our sins. But the day has passed for superficial patriotism. He who lives with untruth lives in spiritual slavery. Freedom is still the bonus we receive for knowing the truth. "Ye shall know the truth," says Jesus, "and the truth shall set you free." Now, I've chosen to preach about the war in Vietnam because I agree with Dante, that the hottest places in hell are reserved for those who in a period of moral crisis maintain their neutrality. There comes a time when silence becomes betrayal.

Orthodoxy (1884)
Context: If the devil had written upon the subject of slavery, which side would he have taken? Let every minister answer. If you knew the devil had written a work on human slavery, in your judgment, would he uphold slavery, or denounce it? Would you regard it as any evidence that he ever wrote it, if it upheld slavery? And yet, here you have a work upholding slavery, and you say that it was written by an infinitely good God!

From Letters from a Farmer, in Pennsylvania, to the inhabitants of the British Colonies, Letter XII, Dickinson, Philadelphia

"Subduing the Rebellion" (22 January 1862), as quoted in The Selected Works of Thaddeus Stevens http://books.google.com/books?id=A0Fs655TKfsC&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false
1860s

Reply to James R. Gilmore, 1864
1860s