“Ridicule is man's most potent weapon.”

Statement quoted in the Boston Globe (25 October 1977)
Context: Even today, we are still accused of racism. This is a mistake. We know that all interracial groups in South Africa are relationships in which whites are superior, blacks inferior. So as a prelude whites must be made to realize that they are only human, not superior. Same with blacks. They must be made to realize that they are also human, not inferior.

The Tragic Sense of Life (1913), Conclusion : Don Quixote in the Contemporary European Tragi-Comedy
Context: Don Quixote made himself ridiculous; but did he know the most tragic ridicule of all, the inward ridicule, the ridiculousness of a man's self to himself, in the eyes of his own soul? Imagine Don Quixote's battlefield to be his own soul; imagine him to be fighting in his soul to save the Middle Ages from the Renaissance, to preserve the treasure of his infancy; imagine him an inward Don Quixote, with a Sancho at his side, inward and heroic too — and tell me if you find anything comic in the tragedy.

Letter to Francis Adrian Van der Kemp (30 July 1816), denouncing the doctrine of the Trinity.
1810s
Context: Ridicule is the only weapon which can be used against unintelligible propositions. Ideas must be distinct before reason can act upon them; and no man ever had a distinct idea of the trinity. It is the mere Abracadabra of the mountebanks calling themselves the priests of Jesus.

Un Art de Vivre (The Art of Living) (1939), The Art of Loving

Source: De architectura (The Ten Books On Architecture) (~ 15BC), Book II, Chapter VIII, Sec. 10
Context: At Halicarnassus, the house of that most potent king Mausolus, though decorated throughout with Proconnesian marble, has walls built of brick which are to this day of extraordinary strength, and are covered with stucco so highly polished that they seem to be as glistening as glass. That king did not use brick from poverty; for he was choke-full of revenues, being ruler of all Caria.

Robert Barry, cited in: Lucy R. Lippard, Six Years: The Dematerialization of the Art Object from 1966 to 1972. New York, Praeger, 1973, p. 40.

Source: Clockwork Angel

As quoted in Notes for a Memoir : On Isaac Asimov, Life, and Writing (2006) by Janet Jeppson Asimov, p. 58
General sources
Variant: Properly read, the Bible is the most potent force for atheism ever conceived.
Context: If you suspect that my interest in the Bible is going to inspire me with sudden enthusiasm for Judaism and make me a convert of mountain‐moving fervor and that I shall suddenly grow long earlocks and learn Hebrew and go about denouncing the heathen — you little know the effect of the Bible on me. Properly read, it is the most potent force for atheism ever conceived.