The conservative has but little to fear from the man whose reason is the servant of his passions, but let him beware of him in whom reason has become the greatest and most terrible of the passions. These are the wreckers of outworn empires and civilisations, doubters, disintegrators, deiciders.

J.B.S. Haldane (1892-1964) English geneticist [John Burden Sanderson Haldane]

“Daedalus, or Science and the Future,” speech, Cambridge (24 Feb 1923)
    (Source)