When a fact can be demonstrated, force is unnecessary; when it cannot be demonstrated, an appeal to force is infamous. In the presence of the unknown all have an equal right to think.

Robert Green Ingersoll (1833–1899) American lawyer, freethinker, orator

Lecture (1873-12) “Individuality,” Chicago Free Religious Society
    (Source)

Full title "Arraignment of the Church and a Plea for Individuality." Collected in The Gods and Other Lectures (1876).