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 . . . .

Such an outlook is quite congenial to an individualistic 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.

--Pope Saint John Paul II, Veritatis Splendor