If the weakness of the head were an admissible excuse for the malevolence of the heart, the one-half of mankind would be occupied in aggression, and the other half in forgiveness; but the interests of society peremptorily demand that things should not be so; for a fool is often as dangerous to deal with as a knave, and always more incorrigible.

Charles Caleb "C. C." Colton (1780-1832) English cleric, writer, aphorist
Lacon: Or, Many Things in Few Words, Vol. 1, § 372 (1820)
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For more about evil vs. stupidity, see also Camus (1947), Catton (1953), and Hanlon (1980).