A theory that is afraid of investigation is undeserving a place in the human mind.

ingersoll - a theory that is afraid of investigation is undeserving a place in the human mind - wist.info quote

Robert Green Ingersoll (1833-1899) American lawyer, freethinker, orator
Lecture (1877-06-23), “The Ghosts,” Carson Theater, Carson City, Nevada
    (Source)

Collected in The Ghosts, and Other Lectures (1878)