Who could have the conceit, the self-confidence to believe that that is what we should do throughout all the rest of human history?
Letter to Charles Humboldt (mid-1962), p. 64
The Selected Letters of George Oppen (1990)
“Moral certainty is always a sign of cultural inferiority. The more uncivilized the man, the surer he is that he knows precisely what is right and what is wrong. All human progress, even in morals, has been the work of men who have doubted the current moral values, not of men who have whooped them up and tried to enforce them. The truly civilized man is always skeptical and tolerant, in this field as in all others. His culture is based on "I am not too sure."”
418
1940s–present, Minority Report : H.L. Mencken's Notebooks (1956)
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H.L. Mencken 281
American journalist and writer 1880–1956Related quotes

Source: "Speech By Shri Kocheril Raman Narayanan On His Assumption Of Office As President Of India"
Source: Memoirs, North Face of Soho (2006), p. 126

Dedication
Man's Moral Nature (1879)

1780s, Letter to Peter Carr (1787)
Context: He who made us would have been a pitiful bungler, if he had made the rules of our moral conduct a matter of science. For one man of science, there are thousands who are not. What would have become of them? Man was destined for society. His morality, therefore, was to be formed to this object. He was endowed with a sense of right and wrong, merely relative to this.
killing people is bad
"Books" (review column), The Magazine of Fantasy and Science Fiction, December 1968
Non-fiction

Source: 2010s, Marked for Death (2012), Ch. 11: "The Facilitators", pp. 177–178