So far as I can tell, the article in which then-Cardinal Joseph Ratzinger called rock music “the vehicle of anti-religion” was published in German in 1986. In my quick Internet search, I was unable to find an English translation online. You may wish to consult with a research librarian to see if there exists such a translation of “Liturgie und Kirchenmusik” (Communio, 1986). In the meantime, see the article below for an overview of Cardinal Ratzinger’s views on liturgical music.
Update: With thanks to the CAF member who sent the link to me, here is a link to Cardinal Ratzinger’s essay Liturgy and Church Music.
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