6 All the evils which poison men and nations and trouble so many hearts have a single cause and a single source: ignorance of the truth—and at times even more than ignorance, a contempt for truth and a reckless rejection of it. Thus arise all manner of errors, which enter the recesses of men's hearts and the bloodstream of human society as would a plague. These errors turn everything upside down: they menace individuals and society itself.
Source: Ad Petri Cathedram (Vatican.va)