“Every man has a right to his own opinion, but no man has a right to be wrong in his facts.”
Deming Headlight (New Mexico), 6 January 1950, as cited in the Yale Book of Modern Proverbs and at There Are Opinions, And Then There Are Facts; Freakonomics blog post by Fred R. Shapiro http://www.freakonomics.com/2011/08/18/there-are-opinions-and-then-there-are-facts/ (18 August 2011)