A priest responsible for the teaching of other priests and laity for pastoral duties instructed a whole class (that I was a part of ) "if you don't believe that something is a sin then it is not", which of course is false when it comes to things pertaining to natural law.
This comes to me as a pleasant surprise, that the Holy Father would revert to the term, "mortal sin." Ever since the 60's this term has been set aside, and "serious sin" or "grave matter" were used in its place. This is a good sign. Perhaps he is beginning to see that there was a real value in some of the more traditional terminology.
People 30 and under who have attended local parochial schools know very little about the Catholic faith, unfortunately. I know of a catechism teacher who has been leading classes in a large parish in Orange County where 100 students per class is the norm. He has never heard of the perpetual virginity of Our Lady. Never heard of it? How does he qualify for being an instructor? If he doesn't know about it, how can he teach the students about it?
This is all too common nowadays. It stems from a planned obsolescence of doctrine, per se. I went to a Renew 2000 course to become a "facilitator" and the man the parish brought in from New York to teach us said several times during the class that we should avoid the topic of dogma in Renew 2000 meetings. Whenever the discussion group touches on Church teachings, we were specifically told, we were to use these techniques they showed us to steer the group away from the discussion of doctrine.