Divini Illius Magistri §65

⁶⁵ Another very grave danger is that naturalism which nowadays invades the field of education in that most delicate matter of purity of morals. Far too common is the error of those who with dangerous assurance and under an ugly term propagate a so-called sex-education, falsely imagining they can forearm youths against the dangers of sensuality by means purely natural, such as a foolhardy initiation and precautionary instruction for all indiscriminately, even in public; and, worse still, by exposing them at an early age to the occasions, in order to accustom them, so it is argued, and as it were to harden them against such dangers.