Fools are everywhere – the name of this website and title of the book which informs it, and a shorthand for the underlying thesis; that court fools and jesters existed, not literally in every place at all times, but across a breathtaking array of cultures over a few millennia.
But the expression is not of my coining and has a much longer pedigree, being from a letter by Cicero (106-43 BC), and becoming a commonly used phrase in the Middle Ages.
Let’s bring it back into regular usage; next time somebody subjects you to stultifying clap-trap, you can simply sigh and say, ‘Oh dear, stultorum plena sunt omnia…’
Source: Cicero, Epistulae ad Familiares, ed. Glynn Williams (Cambridge, MA: Harvard University Press, 1959), vol. II, IX, xxii, 4