Retired Pope Benedict XVI has published a letter which blames clerical sex abuse on the "all-out sexual freedom" of the 1960s.
He said that cultural and historical change had led to a "dissolution" of morality in Catholicism.
The sexual revolution in the 1960s had led to homosexuality and paedophilia in Catholic establishments, he claimed.
The letter sparked fierce criticism from theologians who claim it is "deeply flawed".
Vatican expert Joshua McElwee said in the National Catholic Reporter: "It does not address structural issues that abetted abuse cover-up, or Benedict's own contested 24-year role as head of the Vatican's powerful doctrinal office."
Some allegations of child sex abuse by priests that have emerged date back to decades before the 1960s, the decade that Pope Benedict claims sparked the abuse crisis.
Julie Rubio, a Catholic theologian, said in a tweet that the letter was "profoundly troubling".
Published in the German Catholic magazine Klerusblatt, the 5,500-word letter is divided into three parts.
The first part presents the "wider social context of the question", lamenting the 1960s as a time when "previously normative standards regarding sexuality collapsed entirely".
He blames sexual films, images of nudity and "the clothing of that time" leading to "mental collapse" and "violence".
At the time of the sexual revolution, "Catholic moral theology suffered a collapse that rendered the Church defenceless against these changes in society", he said.
The sexual revolution led to paedophilia being "diagnosed as allowed and appropriate".
Next, the letter examines how this period affected the "dissolution of the Christian concept of morality", particularly in Catholic educational institutions.
In some cases, bishops "sought to bring about a kind of new, modern" Catholicism and the sexual revolution led to "homosexual cliques" in seminaries.
"Why did paedophilia reach such proportions?" he questions. "Ultimately, the reason is the absence of God."
He says "the death of God in a society" means "the end of freedom" and the solution is to "live by God and unto Him".