“The last temptation is the greatest treason: To do the right deed for the wrong reason.”
Variant: The last act is the greatest treason. To do the right deed for the wrong reason.
Source: Murder in the Cathedral
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T.S. Eliot 270
20th century English author 1888–1965Related quotes
Source: The Phantom Tollbooth

From 1980s onwards, Cosmography (1992)
p. 121 https://books.google.com/books?id=sUTZCwAAQBAJ&pg=PA121
1990s, The Ragamuffin Gospel (1990)

Is Divorce Wrong? (1889)
Context: Marriages are made by men and women; not by society; not by the state; not by the church; not by supernatural beings. By this time we should know that nothing is moral that does not tend to the well-being of sentient beings; that nothing is virtuous the result of which is not good. We know now, if we know anything, that all the reasons for doing right, and all the reasons against doing wrong, are here in this world.

Kansas City Star (7 May 1918)
1910s
Context: The President is merely the most important among a large number of public servants. He should be supported or opposed exactly to the degree which is warranted by his good conduct or bad conduct, his efficiency or inefficiency in rendering loyal, able, and disinterested service to the Nation as a whole. Therefore it is absolutely necessary that there should be full liberty to tell the truth about his acts, and this means that it is exactly necessary to blame him when he does wrong as to praise him when he does right. Any other attitude in an American citizen is both base and servile. To announce that there must be no criticism of the president, or that we are to stand by the president, right or wrong, is not only unpatriotic and servile, but is morally treasonable to the American public. Nothing but the truth should be spoken about him or any one else. But it is even more important to tell the truth, pleasant or unpleasant, about him than about any one else.

“Treason doth never prosper: what's the reason?
Why, if it prosper, none dare call it treason.”
Epigrams, Book iv, Epistle 5. Compare: "Prosperum ac felix scelus/ Virtus vocatur" ("Successful and fortunate crime/ is called virtue"), Seneca, Herc. Furens, ii. 250.

"The Ethics of Human Beings Toward Non-human Beings", pp. 278
The Universal Kinship (1906), The Ethical Kinship