Heresy denies the doctrine, and the pope has not denied it. Rather, he has tried to offer a lax application of the doctrine
According to Veritatis Splendor a mortal sin is a mortal sin and the external action indicates the subjective state.If a women is dressed immodestly it is a mortal sin.The outer action indicates the inner state of the soul.
If a couple are living together who are not married it is a mortal.There is scandal.
Father Bernard Haring and Fr.Richard Cushing both Redemptorist priests said NO.
They presented many exceptions, theoretical possibilities which they considered exceptions to the tradtional moral understanding of the Catholic Church. For them exception proved the rule wrong.
They also speculated that within each person there is a Fundamental Option for good and even though the external action was a mortal sin, interiorly the soul was not in sin or to blame.They called this the Fundamental Option Theory.It is specifically mentioned in Veritatis Splendor and is criticised.
So when Pope Francis supports the Fundamental Option Theory in Amoris Laetitia he is striking at the doctrine.There is a new doctrine which has a new application.
Even after Veritatis Splendor was issued the liberals and Masons continued to teach the Fundamental Option Theory at the Pontifical universities in Rome. The books of Fr. Charles Curran ,I noticed, were available in the reference section of the University of St. Thomas Aquinas in Rome.-Lionel Andrades