Your understanding of Roman Catholic moral theology seems to me to be deficient insofar as you seem no to take into account the psychology of the individual when determining whether or not impediments may exist that reduce culpability-something which the Church does in fact do. Furthermore, there are many who are ignorant of the fact that the Church teaches that contraception is a matter of grave matter.
The Church’s teaching with respect to what constitutes mortal sin is not nearly so black-and-white as you seem to want it to be. Even your remark that counseling people that a sin of grave matter is acceptable is itself a mortal sin is problematic without being qualified. If the person who gives such counsel is not aware that grave matter is involved, then it is not a matter of mortal sin. So, please stop saying, “Such and such a sin is mortal sin.”
There is no list of sins that are automatically mortal. There are acts that automatically involve grave matter, but it is not up to you or to me to say that they are automatically mortal. That determination belongs to God, and God alone. The individual penitent must determine, with the guidance of his confessor, by Church teaching, through examination of conscience, and finally, with God’s guidance received through prayer, whether individual acts involving grave matter are indeed a matter of mortal sin.