“Beware the leader who bangs the drums of war in order to whip the citizenry into a patriotic fervor, for patriotism is indeed a double-edged sword. It both emboldens the blood, just as it narrows the mind.”
—Snopes entry

I found a reference to the quote in a work by Dr. Kevorkian called Medical Research and the Death Penalty: A Dialogue, first published in 1960 and revised in 1983.