Giancarlo Livraghi published El poder de la estupidez (The Power of Stupidity) in 2012. These are among the quotations he provides.

“There is no such thing as an underestimate of average intelligence.” Henry Adams

“Scientists will eventually stop flailing around with solar power and focus their efforts on harnessing the only truly unlimited source of energy on the planet: stupidity.” Scott Adams

“I read the newspaper avidly. It is my one form of continuous fiction.” Aneurin Bevan

“However big the fool, there is always a bigger fool to admire him.” Nicolas Boileau

“In politics stupidity is not a handicap.” Napoleon Bonaparte

“There is no opinion so stupid that it can’t be expressed by some philosopher.” Marcus Tullius Cicero

“Man is stupid, phenomenally stupid.” Fyodor Dostoievsky

“The number of fools is infinite.” Ecclesiastes

“Two things are infinite, the universe and human stupidity. I’m not sure about the universe.” Albert Einstein

“The dumbest people I know are those who know it all.” Malcolm Forbes

“If a million people believe a foolish thing, it is still a foolish thing.” Anatole France

“Half the world is composed of people who have something to say and can’t, the other half who have nothing to say and keep on saying it.” Robert Frost

“There is nothing worse than aggressive stupidity.” Johann Goethe

“There are more fools in the world than there are people.”
Heinrich Heine

“Never underestimate the power of human stupidity.” Robert Heinlein

“Nothing in all the world is more dangerous than sincere ignorance and conscientious stupidity.”
Martin Luther King

“The first method for estimating the intelligence of a ruler is to look at the men he has around him.”
Niccolò Machiavelli

“We are drowning in information but starved for knowledge.” John Naisbitt

“If you want to avoid seeing an idiot, break the mirror. François Rabelais

“A fashion is nothing but an induced epidemic.” George Bernard Shaw

“It ain’t what you don’t know that gets you into trouble, it’s what you know for sure that just ain’t so.” Artemus Ward and/or Mark Twain

“Doubt is uncomfortable, certainty is ridiculous.” Voltaire

“Some scientists claim that hydrogen, because it is so plentiful, is the basic building block of the universe. I dispute that. I say there is more stupidity than hydrogen, and that is the basic building block of the universe.” Frank Zappa