And he rightly points the finger to the lack of evangelization on this matter.
To that end, he produced a PDF document to indicate those passages in Scripture that condemn fornication. He explains:
As I have noted, the Biblical word “fornication” is the word that corresponds to what we call today “premarital sex.” Hence, “Fornicator” means one one engages in premarital sex. There are a very few places in the Scriptures where the word fornication (in Greek Porneia) is understood to mean sexual misconduct in general. But usually fornication simply means premarital sex since there are other terms for adultery (moichao); and homosexual acts (arsenkoites).
I think that with many teachings, the Church assumed that they would be transmitted through the ambient culture.
We can no longer take the culture for granted on absolutely ANY teaching. From belief in God, to the existence of Jesus to any single moral issue. ANY issue.
But it's not just a question of teaching. Because you can be very reductionist about teachings. Some people think that as long as you don't engage in a potentially life-giving act, it's not sex (like Bill Clinton claimed).
The issue is also of creating an environment where Catholic teaching is PRACTICED. If Msgr Pope went to the seminary not knowing basic truths of the Catholic faith, it's because his environment didn't teach him those truths.