The Erroneous Moral Theories of Consequentialism and Proportionalism
The need for a sufficient proportion of good effects in order to tolerate the evil effects using the Principle of Double Effect must be distinguished from the condemned moral theories of consequentialism and proportionalism.
Popular especially among European and American theologians after Vatican II, they argued that in determining moral lawfulness the end (intention) could justify an otherwise evil act (proportionalism), or the foreseen good effects could justify an action that previously has been judged to be morally evil.
These theories denied that any act was intrinsically evil by its object alone, apart from its intention and circumstances. Even abortion, contraception, adultery, and other intrinsic evils, which the entire moral tradition has condemned, could, in some cases, be morally good by reason of their intention or consequences.
Pope St. John Paul II, in his Encyclical Veritatis Splendor, specifically condemned these theories.
Veritatis Splendor 75
… “consequentialism” or “proportionalism.” The former claims to draw the criteria of the rightness of a given way of acting solely from a calculation of foreseeable consequences deriving from a given choice. The latter, by weighing the various values and goods being sought, focuses rather on the proportion acknowledged between the good and bad effects of that choice, with a view to the “greater good” or “lesser evil” actually possible in a particular situation.
The teleological ethical theories (proportionalism, consequentialism), while acknowledging that moral values are indicated by reason and by Revelation, maintain that it is never possible to formulate an absolute prohibition of particular kinds of behavior which would be in conflict, in every circumstance and in every culture, with those values.
Veritatis Splendor 76
… Such theories, however, are not faithful to the Church’s teaching, when they believe they can justify, as morally good, deliberate choices of kinds of behavior contrary to the commandments of the divine and natural law. These theories cannot claim to be grounded in the Catholic moral tradition. … The faithful are obliged to acknowledge and respect the specific moral precepts declared and taught by the Church in the name of God, the Creator and Lord.