From Pope St. John Paul II’s encyclical Fides et Ratio (1984):
Another threat to be reckoned with is scientism. This is the philosophical notion which refuses to admit the validity of forms of knowledge other than those of the positive sciences; and it relegates religious, theological, ethical and aesthetic knowledge to the realm of mere fantasy. In the past, the same idea emerged in positivism and neo-positivism, which considered metaphysical statements to be meaningless. Critical epistemology has discredited such a claim, but now we see it revived in the new guise of scientism, which dismisses values as mere products of the emotions and rejects the notion of being in order to clear the way for pure and simple facticity. Science would thus be poised to dominate all aspects of human life through technological progress. The undeniable triumphs of scientific research and contemporary technology have helped to propagate a scientistic outlook, which now seems boundless, given its inroads into different cultures and the radical changes it has brought.
Regrettably, it must be noted, scientism consigns all that has to do with the question of the meaning of life to the realm of the irrational or imaginary. No less disappointing is the way in which it approaches the other great problems of philosophy which, if they are not ignored, are subjected to analyses based on superficial analogies, lacking all rational foundation. This leads to the impoverishment of human thought, which no longer addresses the ultimate problems which the human being, as the animal rationale, has pondered constantly from the beginning of time. And since it leaves no space for the critique offered by ethical judgement, the scientistic mentality has succeeded in leading many to think that if something is technically possible it is therefore morally admissible.
— Fides et Ratio 88