“Those kind friends who suggest to a person suffering from a tedious complaint, that he "Had better try Homoeopathy," are apt to enforce their suggestion by adding, that "at any rate it can do no harm." This may or may not be true as regards the individual. But it always does very great harm to the community to encourage ignorance, error, or deception in a profession which deals with the life and health of our fellow-creatures.”

Variant translation: If someone is able to show me that what I think or do is not right, I will happily change, for I seek the truth, by which no one ever was truly harmed. Harmed is the person who continues in his self-deception and ignorance.
VI, 21
Source: Meditations (c. 121–180 AD), Book VI

Source: Alice's Adventures in Wonderland

Source: Meditations

Our Country at the Crossroads - 2001 Parkinson Memorial Lecture Series, 15 August 2001 http://www.usp.ac.fj/journ/docs/news/wansolnews/wansol1508013.html.

Source: Outsiders: Studies in the Sociology of Deviance (1963), pp. 1-2.

The Plague (1947)
Context: The evil that is in the world always comes of ignorance, and good intentions may do as much harm as malevolence, if they lack understanding. On the whole men are more good than bad; that, however, isn't the real point. But they are more or less ignorant, and it is this that we call vice or virtue; the most incorrigible vice being that of an ignorance which fancies it knows everything and therefore claims for itself the right to kill. There can be no true goodness, nor true love, without the utmost clear-sightedness.

Source: Gone Girl

Quoted in Tales of the Mystic East: An Anthology of Mystic and Moral Tales Taken from the Teachings of the Saints (Radha Soami Satsang Beas, 1997), p. 208

"Religion: A Dialogue."
Variant translation: To free a man from error does not mean to take something from him, but to give him something.
Essays
Source: Essays and Aphorisms
Context: To free a man from error is to give, not to take away. Knowledge that a thing is false is a truth. Error always does harm; sooner or later it will bring mischief to the man who harbors it. Then give up deceiving people; confess ignorance of what you don't know, and leave everyone to form his own articles of faith for himself. Perhaps they won't turn out so bad, especially as they'll rub one another's corners down, and mutually rectify mistakes. The existence of many views will at any rate lay a foundation of tolerance. Those who possess knowledge and capacity may betake themselves to the study of philosophy, or even in their own persons carry the history of philosophy a step further.