A major source of philosophical and moral error in our age arises from a perverse distortion of human freedom. Having denied that there are any absolutes, man is left to himself to choose what he will believe and how he will live, as though just anything he might select is thereby validated. Pope John Paul II has this to say about this problem in VS §32:
Certain currents of modern thought have gone so far as to exalt freedom to such an extent that it becomes an absolute, which would then be the source of values. This is the direction taken by doctrines which have lost the sense of the transcendent or which are explicitly atheist. The individual conscience is accorded the status of a supreme tribunal of moral judgment which hands down categorical and infallible decisions about good and evil. To the affirmation that one has a duty to follow one’s conscience is unduly added the affirmation that one’s moral judgment is true merely by the fact that it has its origin in the conscience. But in this way the inescapable claims of truth disappear, yielding their place to a criterion of sincerity, authenticity and “being at peace with oneself”, so much so that some have come to adopt a radically subjectivistic conception of moral judgment.
As is immediately evident, the crisis of truth is not unconnected with this development. Once the idea of a universal truth about the good, knowable by human reason, is lost, inevitably the notion of conscience also changes. Conscience is no longer considered in its primordial reality as an act of a person’s intelligence, the function of which is to apply the universal knowledge of the good in a specific situation and thus to express a judgment about the right conduct to be chosen here and now. Instead, there is a tendency to grant to the individual conscience the prerogative of independently determining the criteria of good and evil and then acting accordingly. Such an outlook is quite congenial to an individualist ethic, wherein each individual is faced with his own truth, different from the truth of others. Taken to its extreme consequences, this individualism leads to a denial of the very idea of human nature.
These different notions are at the origin of currents of thought which posit a radical opposition between moral law and conscience, and between nature and freedom. [Emphasis in original]
Unfortunately this poisonous “freedom” has infected even many in the Church. But the Catholic who rejects what the Church teaches has to that extent ceased to be Catholic, and as St Thomas says does not even have the theological virtue of faith at all.
Neither living nor lifeless faith remains in a heretic who disbelieves one article of faith.
The reason of this is that the species of every habit depends on the formal aspect of the object, without which the species of the habit cannot remain. Now the formal object of faith is the First Truth, as manifested in Holy Writ and the teaching of the Church, which proceeds from the First Truth. Consequently whoever does not adhere, as to an infallible and Divine rule, to the teaching of the Church, which proceeds from the First Truth manifested in Holy Writ, has not the habit of faith, but holds that which is of faith otherwise than by faith. Even so, it is evident that a man whose mind holds a conclusion without knowing how it is proved, has not scientific knowledge, but merely an opinion about it. Now it is manifest that he who adheres to the teaching of the Church, as to an infallible rule, assents to whatever the Church teaches; otherwise, if, of the things taught by the Church, he holds what he chooses to hold, and rejects what he chooses to reject, he no longer adheres to the teaching of the Church as to an infallible rule, but to his own will. Hence it is evident that a heretic who obstinately disbelieves one article of faith, is not prepared to follow the teaching of the Church in all things; but if he is not obstinate, he is no longer in heresy but only in error. Therefore it is clear that such a heretic with regard to one article has no faith in the other articles, but only a kind of opinion in accordance with his own will. [ST II-II q5 a3; emphasis added]
There is no exercise of faith in the man who “obstinately disbelieves one article of faith.” So (for one dreadful example) a husband and wife who use contraception despite knowing that to do so is contrary to the teaching of the Church have lost faith entirely: if they agree with the Church’s teaching on other things it is nothing more than a happy coincidence. Obviously this is not what it means to be Catholic, and we must unconditionally reject the temptation of our age to do or think otherwise. We are not free to decide for ourselves what is true; we are not free to declare what is good or evil in moral conduct.