1. There are many thinkers who are in various ways very close and very distant from Catholicism in recent philosophy. One reads Nietzsche, for example, and Nietzsche's thought is excellent for clarifying certain metaphysical problems in modern thought. Heidegger makes a wonderful critique of modern epistemology and, to some extent, technological life. Wittgenstein shows negatively the inadequacy of logical atomism. Foucault perfects Nietzschean genealogy.
2. All of these are very useful. At the present moment one can take them and use them in either of two distant ways. One tendency is to take them as a new foundation for theological reflection. Thus we have the phenomenological anthropocentric Christianity of the Christian (and Catholic) Heideggerians, and the work of the 20th century Christian Existentialists, and the various "genitive" and cultural theologies. And on the other hand we have the genealogical work of scholars like Cornelio Fabro and Joseph Ratzinger, who, while maintaining an authentically Catholic outlook in their principles and in every particular, attempt to use insights from these traditions to understand the present state of liberalism and the trajectory of modern secular thought's decay, and to bolster the response of Catholic thought to the present age.
3. When one encounters too many thinkers of the first variety, one is sometimes tempted to throw out these secular writers as trash, on account of their fundamental errors. Certainly they are not fitting masters from which to receive a basic orientation or instruction in the first principles of philosophy or theology. They are not the right people to use when framing one's outlook as a Christian, or understanding the proper method for philosophical procedure.
4. But (is it strange to say?) it would be a terrible loss never to read Nietzsche or Heidegger. Not because Heidegger's Seinsfrage is the right theme for philosophy, or because we should hope for the advent of the Übermensch, but because in their discussion of various particular themes they speak with an alacrity and beauty difficult to outdo. Among apostates and pagans there is wisdom too! We should take the spoils of Egypt with us in our flight to the Promised Land—not to make idols of them in the desert, not to be turned by them to despair and wish for the land of our captors, but to put them to good use, to melt them down and purify them, and use them to adorn the temple of the true God.
5. This was true for the Fathers. It is true for us today as well.