The term intrinsic evil is a technical term. It has a precise meaning which is based on the theology of sin.
Now for a Catholic there are three conditions which must apply for a sin to be a mortal sin. They are:
- The sin must involve a grave matter.
- The sin must be committed with the full knowledge of the sinner.
- The sin is committed with the full consent of the sinner.
The person must understand that the act is a sin. (This goes to another concept called vincible ignorance which I will not discuss here.)
The person must consent to the sin. A coerced act will not be a mortal sin.
It becomes obvious that many types of mortal sin are conditional. That is the conditions which surround the act determine whether or not it is a sin. When there is a disagreement about whether or not something is a sin and the Church has not taken a stance then the subject is said to be relegated to the prudential judgment of the faithful. The best way to fight poverty is a matter for prudential judgment, although there are methods, socialism, liberation justice methods and others which the Church has spoken out against due to their negative impact on human dignity.
There are a number of sins which the Church has declared are not open to prudential judgment. These acts are always sinful, irregardless of the situation. They are called intrinsically evil sins. The modern Church recognized five such classes of sins. Three of them have always been opposed by the Church from time immemorial. The other two are the fruits of modern science.
These sins are:
- Support for the normalization of intrinsically disordered sexual licentiousness.
- Allowing innocent babies to be conceived for the purpose of scientific study or harvesting their parts, as in stem cell research.
- Manipulating human DNA for the purpose of "improving" or duplicating another human being, as in cloning.
A Catholic politician can not support any law which support any of these acts, nor can the any member Catholic faithful vote for any politician who has voted for such a law without themselves committing a mortal sin. That is not my opinion, but the opinion of the Holy Father.
There are no other acts by such a politician, no stand on another issue that makes it alright to vote for such a politician.
Politics is call the art of the possible. It expects compromise might sometimes be necessary in order to reach certain goal. Vote for a bad policy so that a greater good can be achieved.
Salvation does not work like that. It is never permissible to support an elected official who supports an intrinsic evil.
Note this does not mean that it is alright to vote for an opposing politician who would support torture or unjust war or racism. These are acts which are not intrinsically evil, but which are also sins because they impinge on the fundamental dignity of the human person.
The right of a nation to employ capital punishment has always been supported by the church. The Holy Father has said that in modern western society he believes that the use of capital punishment is unnecessary. This is a prudential judgment, and as the Holy Father himself has said it is neither morally equivalent to abortion, nor is support for a candidate who supports capital punishment a sin.
This is not a political fact it is a theological fact.
Could it be then that there may be no candidate in an election for which a Catholic can morally vote. Indeed that can be the case.
If there are two candidates in a race, one of whom is committed to expanding and ensuring the right of abortion under all circumstances, and one of who is committed to reducing the number of abortions while maintaining the "right" of women to kill their unborn babies it is permissible to vote for the second candidate, provided the vote is in spite of their stand on abortion, rather than in support of it.
In an election in which one candidate is a supporter of abortion and the other a foe of abortion, but would support the use of torture, then the prudential Catholic could not, in good conscious, that is without sin, vote for either of the candidates.
If we compromise on evil we sin.