Whoever has an opinion of his own, and honestly expresses it, will be guilty of heresy. Heresy is what the minority believe; it is the name given by the powerful to the doctrine of the weak.

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

Lecture (1874-05-03), “Heretics and Heresies,” Free Religious Society, Kingsbury Hall, Chicago
    (Source)

Collected in The Gods and Other Lectures (1876).