“Most people agree that slavery is immoral. But what makes it so? Slavery denies a person the right to use his property (body) and the fruits of his labor the way he sees fit. Slavery forcibly uses one person to serve the purposes of another. Tragically, most Americans, including blacks, whose ancestors have suffered from gross property right violations, think it quite proper that one person be forcibly used to serve the purposes of another.”

As quoted in "Lincoln's Nuanced View of Slavery Explained By Renowned Historian" https://www.registercitizen.com/news/article/Lincoln-s-nuanced-view-of-slavery-explained-by-12077170.php, by Michelle Merlin, The Register Citizen (9 August 2012)
2010s

1860s, The Constitution of the United States: Is It Pro-Slavery or Anti-Slavery? (1860)
Context: I, on the other hand, deny that the Constitution guarantees the right to hold property in man, and believe that the way to abolish slavery in America is to vote such men into power as well use their powers for the abolition of slavery. This is the issue plainly stated, and you shall judge between us.

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

Der ganze Unterschied gegen die alte, offenherzige Sklaverei ist nur der, dass der heutige Arbeiter frei zu sein scheint, weil er nicht auf einmal verkauft wird, sondern stückweise, pro Tag, pro Woche, pro Jahr, und weil nicht ein Eigenthümer ihn dem andern verkauft, sondern er sich selbst auf diese Weise verkaufen muss, da er ja nicht der Sklave eines Einzelnen, sondern der ganzen besitzenden Klasse ist.
Source: (1845), pp. 114-115

The Virtue of Selfishness (1964)

An Address on Abraham Lincoln before the Republican Club of New York City (12 February 1909) http://web.archive.org/20050322051431/www.historycooperative.org/btw/Vol.10/html/35.html
Context: Of all forms of slavery there is none that is so harmful and degrading as that form of slavery which tempts one human being to hate another by reason of his race or color. One man cannot hold another man down in the ditch without remaining down in the ditch with him.

Letter to General Marquis de Lafayette https://archive.org/stream/jstor-2713830/2713830_djvu.txt (25 November 1820), Montpelier
1820s
Context: The subject which ruffles the surface of public affairs most, at present, is furnished by the transmission of the "Territory" of Missouri from a state of nonage to a maturity for self-Government, and for a membership in the Union. Among the questions involved in it, the one most immediately interesting to humanity is the question whether a toleration or prohibition of slavery Westward of the Mississippi would most extend its evils. The human part of the argument against the prohibition turns on the position, that whilst the importation of slaves from abroad is precluded, a diffusion of those in the Country tends at once to meliorate their actual condition, and to facilitate their eventual emancipation. Unfortunately, the subject, which was settled at the last session of Congress by a mutual concession of the parties, is reproduced on the arena by a clause in the Constitution of Missouri, distinguishing between free persons of colour and white persons, and providing that the Legislature of the new State shall exclude from it the former. What will be the issue of the revived discussion is yet to be seen. The ease opens the wider field, as the Constitution and laws of the different States are much at variance in the civic character giving to free persons of colour; those of most of the States, not excepting such as have abolished slavery, imposing various disqualifications, which degrade them from the rank and rights of white persons. All these perplexities develop more and more the dreadful fruitfulness of the original sin of the African trade.

Undated manuscript outline of a sermon on "Cooperative/Noble Competition" http://www.thekingcenter.org/archive/document/cooperativenoble-competition, at the King center; King takes Luke 22:24 as the basis of this message.
Context: Jesus himself saw the power that competition hold over men, He did not ignore it. Yet he does something with the conception of competition that had it been done before. He takes the conception, which has been used for lower purposes and rescues it from many of its dangers, by suggesting a higher method of its use. This is how he applied the term to his disciples. He saw them in danger of using it for low purposes. They wanted to complete for reputation and position. Which of them should be accepted greatest? Jesus say so, if you must use the power of competition, if you must compete with one another: make it as noble as you can by using it [in] noble things. Use it for a fine unselfish thing. He that is greatest among you shall serve. Use it for human good. Shall be the most useful; compete with one another in humility. See which can be the truest servant. It seems that Christ says — use it but use it for higher and holier purpose. Use it not to surpass one another in esteem, but use it to increase the comment of usefulness and brother’s help...
Imagine the change that would come about if the Churches applied this truth. Now we are bogged not in competitive denominationalism, which is a destroying the warm blood of Protestant Church. Which of them shall be accounted greatest? Let the churches stop trying to outstrip each other in the number of their adherents, the size of its sanctuary, the abundance of wealth. If we must compete let us compete to see which can move toward the greatest attainment of truth, the greatest service of the poor, and the greatest salvation of the soul and bodies of men.
Suppose the teaching of Jesus should be accepted by competing nations of the world, particularly Russia and Am[er]ica. They would no longer compete to see which could make the bigger atom bombs, or which cold best perpetuate its imperialism, but which could best serve humanity. This would be a better world.