In the reply above I try to show that a more fundamental motive lurks behind the suggested oppostion between faith and reason. This motive is a religious freedom ideal. It seems that in the history of ethics, the term happiness appears to be replaced by the term freedom.
Like Aristotle said, it is generally agreed that what fulfills the human purpose is called happiness. He also said there are several candidates for that fulfillment, but however conceived, it is called a state of happiness (eudaimonia). In Latin it became beatitude after Augustine.
But now in the West the label appears to be freedom. It is no coincidence that in the West the conception of human happiness is conceived of in terms of freedom.
Asking the same ethical question that arises in Aristotle, --What is the motive behind human action? -- To obey reason or to be free? To be free and reasonable? These were some of the questions Kant took up. In his answer he conceived the happy harmony of reason and freedom by making them one and the same. Which is not freedom, for it means nothing but the enslavement of oneself to reason-imposed duty. This is often nicely called self-actualization. What was left of God was not his existence but a mere a postulate for the possibility of freedom. That was in Germany. For self-actualization in France there was Rousseau. Man is everywhere in chains. He preferred to give natural development its free course. In both cases, freedom was the final term that would make their answers credible.
If this is even a near-legitimate sketch, the opposition suggested by the labels of faith and reason in this context are not at all what humanae vitae has in mind. For faith and reason in the context above are oppositions based on a freedom ideal where now either reason is ascendant or nature is ascendant. The reiteration of the opposition obscures the particular religious motive of freedom that frames the debate.
If the Middle Ages had left the Europeans anything, it was the fulfillment of human happiness in another world. If the Renaissance had left the Europeans anything, it was happiness in this world. There is no way to conceive of a happiness that has one living in both worlds at once.
And yet here is the suggestion that we could grow one leg on faith and another leg on reason.
The opposition of faith and reason is a direct result from the sidelining of happiness conceived a-historically. A close reading of Kant's ethics will make clear how the shift begins to take place: God no longer exists, he is the deduced postulate for the possibility of human freedom. His Kingdom of Ends is but a leftover from the old world. We don't know where it is because Kant has abandoned history for the nature-science ideal.
I apologize for giving this answer without citations. I think that citations would make this clearer.
You and I see many of the same facts but give somewhat different accounts of the enlightenment, freedom, reason, and faith. Hopefully tomorrow I'll have time to give you an outline of my account.
Thanks again.