"If I let myself believe anything on insufficient evidence, there may be no great harm done by the mere belief; it...

"If I let myself believe anything on insufficient evidence, there may be no great harm done by the mere belief; it may be true after all, or I may never have occasion to exhibit it in outward acts. But I cannot help doing this great wrong towards Man, that I make myself credulous. The danger to society is not merely that it should believe wrong things, though that is great enough; but that it should become credulous, and lose the habit of testing things and inquiring into them; for then it must sink back into savagery."
-- William Kingdon Clifford (mathematician & philosopher, 1845-1879)
http://en.wikipedia.org/wiki/William_Kingdon_Clifford