“However, some things must be said, and there are times when silence becomes an accomplice to injustice.”

Source: Sister Carrie

1960s, Beyond Vietnam: A Time to Break Silence (1967)
Context: Even when pressed by the demands of inner truth, men do not easily assume the task of opposing their government's policy, especially in time of war. Nor does the human spirit move without great difficulty against all the apathy of conformist thought within one's own bosom and in the surrounding world. Moreover, when the issues at hand seem as perplexing as they often do in the case of this dreadful conflict, we are always on the verge of being mesmerized by uncertainty; but we must move on.
And some of us who have already begun to break the silence of the night have found that the calling to speak is often a vocation of agony, but we must speak. We must speak with all the humility that is appropriate to our limited vision, but we must speak.
Context: Even when pressed by the demands of inner truth, men do not easily assume the task of opposing their government's policy, especially in time of war. Nor does the human spirit move without great difficulty against all the apathy of conformist thought within one's own bosom and in the surrounding world. Moreover, when the issues at hand seem as perplexing, as they often do in the case of this dreadful conflict, we're always on the verge of being mesmerized by uncertainty. But we must move on. Some of us who have already begun to break the silence of the night have found that the calling to speak is often a vocation of agony. But we must speak. We must speak with all the humility that is appropriate to our limited vision, but we must speak. And we must rejoice as well, for in all our history there has never been such a monumental dissent during a war, by the American people.

On Nature, as quoted by Friedrich Ueberweg, History of Philosophy, from Thales to the Present Time (1885) Vol. 1, p. 35. https://books.google.com/books?id=BW5YAAAAMAAJ&pg=PA35

A response to the Nazi book burnings, in "To Posterity" (1939) as translated by H. R. Hays (1947)
Context: Do not treat me in this fashion. Don't leave me out. Have I not
Always spoken the truth in my books? And now
You treat me like a liar! I order you:
Burn me!
Those who lead the country into the abyss
Call ruling too difficult
For ordinary men.
Ah, what an age it is
When to speak of trees is almost a crime
For it is a kind of silence about injustice!

Antisthenes, 4.
The Lives and Opinions of Eminent Philosophers (c. 200 A.D.), Book 6: The Cynics

Source: This Way for the Gas, Ladies and Gentlemen