Pascal in his polemics against the Jesuits (Cf. his Provincial Letters), accused them of being rascals who attempted to justify moral laxity. Pascal preferred ecclesial law and order, unambiguous. Casuistry, a criticism of one-for-all rule-based reasoning, sought to seriously interpret Catholic principles through the use of other serious Catholic principles: Thou shalt keep Holy the Sabbath Day. Yes. Thou shalt not bear false witness against thy neighbor. Yes.
But the Lord said, the Sabbath was made for man, not man for the Sabbath; therefore in the interests of other true principles (mercy, justice, etc) some things the Pharisees strictly forbade had lost sight of the "weightier matters of the law".
Lying is always wrong. But should I surrender an innocent man to a rope-carrying mob who demands to know whether I am hiding him? Should I send him to a certain death? Most of us agree that in such "simple" instances (simple if we are not the possible objects of the rolling wrath!) we may justify exceptions. Yet in virtually any area of (serious, and I mean serious!) moral anxiety, born of an element of uncertainty, fierce debate kicks up its heels.
This is where a well-formed conscience, seriously informed by the teachings of the Church enters; and sometimes we are left alone with it as all of our serious Christian friends are fist fighting over the hard questions, camp against camp.
Sometimes in the apparent conflict of duties we have no choice but to make an informed decision and to ask God to have mercy. Whether what follows applies at all in this context you and your conscience will have to decide, whatever the outcome as you see it.
Back in the day I had a philosophy professor who posed a classic, wrenching scenario: You and dozens of family members and neighbors are hiding underneath a porch, almost completely concealed from the Jackboots scouring the very street in the village in a search-and-destroy mission against all enemies. All of you are trembling, choked with fear. If found out you are all dead, as certain as the sun will set tonight. The women may be raped and the men tortured before they are murdered. Suddenly the baby the mother is nursing begins to cry, then begins to scream...The baby cannot be quieted but only screams louder and louder, his face purple with discomfort. A man demands, "kill him quickly"! The mother begins to scream. Another man from behind pulls her harshly to the ground and covers her mouth. Her eyes are wild with horror. Yet another man insists, "now give me the child..."