Objectively, the sea is composed of water, objectively, two plus three is five; such truths do not depend on the opinion of every person and they are imposed to every one of us, due to their own evidence. If somebody has an opinion which collides with such reality, we say that the person is wrong, that he or she isn’t in the truth. Is it perhaps only in the moral order where it is not possible to make objective statements (that, deliberately and freely chosen by the will, there are objects which are bad (or good) on themselves)? Would such moral truth only depend on the subjective impressions, on the opinions of everyone?

To realize that in the moral order we can also speak about  an objective order, we can take a very simple example: Is it perhaps not true that it will always be immoral to murder an innocent person? We have an intuitive moral perception, an inborn moral sense which tells us that it is like that. In the same way that our eyes and our experience tell us that the sea is composed of water.

Yet a blind man who has never seen the sea can perhaps sustain that the sea has no water. In the same way, only somebody who has annulled this inner moral vision can sustain that it doesn’t go against moral order to kill an innocent person.

Anyway, as the sea is composed of water, even if one or several persons deny it, to kill an innocent person will always be a cause for moral condemnation. 

It is understood that, if they are carried out with full knowledge and free will, such objectively bad actions will always be bad, whatever the intention might be; so, if one kills an innocent person in order to save another person or even to save a whole nation, such an action will always be a reprehensible crime to the eyes of God.

Thus, in the Catechism, Nº 1573, we can read: “A good intention (helping the neighbour, for instance) doesn’t change a bad behavior into a good or just one (as lying and evil-speaking).The end doesn’t justify the means.So, one cannot justify the condemnation of an innocent person as a legitimate way to save people”.

The moral quality of actions cannot be modified by the circumstances; these cannot change to good or just an action that is bad on itself (although they can increase or decrease its malice)”. (Catechism, Nº 1754)

And Catechism in Nº 1576 ratifies: “There are acts that, aside from circumstances and intentions, are always seriously illicit on themselves because of their object: blasphemy and perjury, homicide and adultery, for instance. It is not allowed to act wrongly in order to obtain good”.

But, what to do when we are tempted and we feel ourselves captives of evil? We should pray and think it over. We are never forsaken by God: “The Holy Spirit makes us differentiate between the test (which is good for our inner development) (…) and temptation, which leads to sin and death (…). Discernment unmasks the falsehood of temptation: apparently, its object is “good”, visually seducing, “desirable” (Gn 3, 6), but, in reality, its consequence is death” (Catechism Nº 2847).