90 More than ever nowadays an extended and careful vigilance is necessary, inasmuch as the dangers of moral and religious shipwreck are greater for inexperienced youth. Especially is this true of impious and immoral books, often diabolically circulated at low prices; of the cinema, which multiplies every kind of exhibition; and now also of the radio, which facilitates every kind of communications. These most powerful means of publicity, which can be of great utility for instruction and education when directed by sound principles, are only too often used as an incentive to evil passions and greed for gain. St. Augustine deplored the passion for the shows of the circus which possessed even some Christians of his time, and he dramatically narrates the infatuation for them, fortunately only temporary, of his disciple and friend Alipius. How often today must parents and educators bewail the corruption of youth brought about by the modern theater and the vile book!
Source: Divini Illius Magistri (Vatican.va)