Tell me, my love, hast though instead chosen Epicurus as thy spouse?
Can Amoris Laetitia confirm in the minds of those living in irregular unions that their choice of life is okay?
A lot has been said about the teaching that a person cannot commit a grave sin without full knowledge and consent needs exploring. Let us explore this idea arriving at two positions (a) one that can justify disordered behaviour by appealing to one's subjective opinion (b) one where there are moral absolutes that cannot be appeased by an appeal to a person’s subjective state of mind or mitigating circumstances.
From a Subjective Perspective
Mortal sin attacks charity. It presupposes knowledge of the sinful character of the act, of its opposition to God's law. It also implies a consent sufficiently deliberate to be a personal choice. Unintentional ignorance can diminish or even remove the imputability of a grave offense, but no one is deemed to be ignorant of the principles of the moral law (Catechism, 1860).
When the will sets itself upon something that is of its nature incompatible with the charity that orients man toward his ultimate end, then the sin is mortal by its very object . . . But when the sinner's will is set upon something that of its nature involves a disorder, but is not opposed to the love of God and neighbour, such sins are venial (Catechism, 1856).
From an Objective Perspective
The object, the intention, and the circumstances make up the "sources," or constitutive elements, of the morality of human acts (Cathechism, 1750).
The object of the choice can by itself vitiate an act in its entirety. There are some concrete acts that are always wrong to choose, because choosing them entails a disorder of the will, that is, a moral evil (Catechism, 1761).
This means circumstances/intentions can never transform an intrinsically evil act into a subjectively good one, but dissenting moral theologians disagree (they now have the title revisionists). This is the battleground for the . . .
The Big Debate
Veritatis Splendor taught that some acts are intrinsically evil by virtue of their object, and that there are moral absolutes that cannot be appeased by an appeal to a person’s subjective state of mind or mitigating circumstance. To grasp the arguments behind this debate see https://www.ewtn.com/library/THEOLOGY/MORALVS.HTM.
From the subjective—from one’s own perspective—we tend to justify anything that we do (see confirmation bias). In that case, can Amoris Laetitia confirm in the minds of those living in irregular unions, that their choice of life is okay and not gravely disordered. If so, Amoris Laetitia kind of has an Epicurean flavour!
Epicurus' ethics is a form of egoistic hedonism; i.e., he says that the only thing that is intrinsically valuable is one's own pleasure; anything else that has value is valuable merely as a means to securing pleasure for oneself (source http://www.iep.utm.edu/epicur/#H3).
To read further about confirmation bias http://www.johnthebaptistmoora.com/346443107/4417966/posting/the-psychology-of-a-sinful-conscience-and-the-danger-posed-by-amoris-l%C3%A6titia