“Selfishness is the bedrock on which all moral behavior starts and it can be immoral only when it conflicts with a higher moral imperative.”
The Pragmatics of Patriotism (1973)
Context: Selfishness is the bedrock on which all moral behavior starts and it can be immoral only when it conflicts with a higher moral imperative. An animal so poor in spirit that he won't even fight on his own behalf is already an evolutionary dead end; the best he can do for his breed is to crawl off and die, and not pass on his defective genes.
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Robert A. Heinlein 557
American science fiction author 1907–1988Related quotes

“The security of Israel is a moral imperative for all free peoples.”
Source: See For the Record: Selected Statements 1977-1980 https://books.google.com.br/books?id=wcx4AAAAMAAJ, Weidenfeld and Nicolson, 1981.

“A moral system valid for all is basically immoral.”
Generally attributed to Nietzsche, this is a quotation from Curtis Cate's Friedrich Nietzsche: A Biography (2003) and is the author's interpretation of Nietzsche's Aphorism 221 (Beyond Good and Evil)
Misattributed

“Fashion is neither moral or immoral, but it is for rebuilding the morale.”

Dr. Whewell on Moral Philosophy (1852), in Dissertations and Discussions: Political, Philosophical, and Historical, vol. 2, London: John W. Parker and son, 1859, p. 485 https://books.google.it/books?id=w-I3AQAAMAAJ&pg=PA485

“Suspending moral judgment is not the immorality of the novel; it is its morality.”
Testaments Betrayed (1995), p. 7
Context: Suspending moral judgment is not the immorality of the novel; it is its morality. The morality that stands against the ineradicable human habit of judging instantly, ceaselessly, and everyone; of judging before, and in the absence of, understanding. From the viewpoint of the novel’s wisdom, that fervid readiness to judge is the most detestable stupidity, the most pernicious evil.

Science and Spirit interview (2004)
Context: We all eat or are eaten. That's the way life works, it's a greater rhythm. And that's why science and the understandings it has uncovered can be a source of joy.
This all relates to assent, a very important Judeo-Christian concept. "Thy will be done" is a God-kind of assent. "God works in mysterious ways," and you're supposed to give assent even if you don't like it. As a religious naturalist, I think of assent differently. Assent is saying, "Okay, for whatever reason, this is the way life works. It's an acceptance of what is. After that fundamental acceptance, I can live my life to minimize suffering and promote as much as good as I can, and try through whatever work I do to help others." We can't get around death, but we can get around poverty. We can try to avoid women being brutalized. We can curb environmental degradation.
One can start from the perspective of a religious naturalist or from the perspective of the world religions and arrive at the same place: a moral imperative that this Earth and its creatures be respected and cherished.

As quoted in "Evolution? No" http://archives.adventistreview.org/2004-1509/story2.html, The Adventist Review (2004)