“Humanity can not be made equal by declarations on paper. Unless the material conditions for equality exist, it is worse than mockery to pronounce men equal.”

Those are undeniable truths.
Vietnamese Proclamation of Independence (2 September 1945), Ho Chi Minh, Selected Works (1960-1962), Vol. 3, pp. 17-21

Alistair Cooke's America (1973)

2000s, Is Diversity Good? (2003)
Context: To allow slavery to be introduced into free territories, where it had not hitherto existed, was, Abraham Lincoln held, a very bad thing. His opponent, Stephen A. Douglas, held that it was a sacred right, belonging to the people of each territory, to decide for themselves whether or not to have slavery among their domestic institutions. According to Douglas, Lincoln wanted to destroy the diversity upon which the union had subsisted, by insisting that all the states ought to be free. But for Douglas himself, the principle of 'popular sovereignty' did not admit of exceptions. There was to be no diversity, no deviation from the right of the people to decide. For Lincoln the wrongness of slavery meant that no one, and no people, had the right to decide in its favor. For Lincoln, the principle of human equality, "that all men are created equal", did not admit exceptions.

12th Annual Report to the Massachusetts State Board of Education http://www.tncrimlaw.com/civil_bible/horace_mann.htm (1848); published in Life and Works of Horace Mann Vol. III, (1868) edited by Mary Mann, p. 669
Context: Education, then, beyond all other devices of human origin, is the great equalizer of the conditions of men, — the balance-wheel of the social machinery. I do not here mean that it so elevates the moral nature as to make men disdain and abhor the oppression of their fellow-men. This idea pertains to another of its attributes. But I mean that it gives each man the independence and the means by which he can resist the selfishness of other men. It does better than to disarm the poor of their hostility towards the rich: it prevents being poor.

1970s, Two Cheers for Capitalism (1978)

Under Fire (1916), Ch. 24 - The Dawn
Context: Paradis, possessed by his notion, waved his hand towards the wide unspeakable landscape. and looking steadily on it repeated his sentence, 'War is that. It is that everywhere. What are we, we chaps, and what's all this here? Nothing at all. All we can see is only a speck. You've got to remember that this morning there's three thousand kilometers of equal evils, or nearly equal, or worse."
"And then," said the comrade at our side, whom we could not recognize even by his voice, "to-morrow it begins again. It began again the day before yesterday, and all the days before that!"

Source: Tristes Tropiques (1955), Chapter 16 : Markets p. 149

Attributed

1910s, The Progressives, Past and Present (1910)
Context: Fundamentally, our chief problem may be summed up as the effort to make men as nearly as they can be made, both free and equal; the freedom and equality necessarily resting on a basis of justice and brotherhood. It is not possible, with the imperfections of mankind, ever wholly to achieve such an ideal, if only for the reason that the shortcomings of men are such that complete and unrestricted individual liberty would mean the negation of even approximate equality, while a rigid and absolute equality would imply the destruction of every shred of liberty. Our business is to secure a practical working combination between the two. This combination should aim, on the one hand to secure to each man the largest measure of individual liberty that is compatible with his fellows getting from life a just share of the good things to which they are legitimately entitled; while, on the other hand, it should aim to bring about among well-behaved, hardworking people a measure of equality which shall be substantial, and which shall yet permit to the individual the personal liberty of achievement and reward without which life would not be worth living, without which all progress would stop, and civilization first stagnate and then go backwards. Such a combination cannot be completely realized. It can be realized at all only by the application of the spirit of fraternity, the spirit of brotherhood. This spirit demands that each man shall learn and apply the principle that his liberty must be used not only for his own benefit but for the interest of the community as a whole, while the community in its turn, acting as a whole, shall understand that while it must insist on its own rights as against the individual, it must also scrupulously safeguard these same rights of the individual.