It occurs to me ed:

Ella Wheeler Wilcox, “Protest”, in "Poems of Problems"
https://www.poets.org/poetsorg/poem/protest
To sin by silence, when we should protest, Makes cowards out of men.


Robert K. Hudnut "A Sensitive Man and the Christ", 1971
Silence in the face of evil is itself evil: God will not hold us guiltless. Not to speak is to speak. Not to act is to act.
(Attributed to Dietrich Bonhoeffer but it is not found in any of his letters or works.)