Darwin Catholic has a long response to Melinda Selmys’s also-long concerns about the moral theology behind the Church’s teaching on contraception. Ferret out the details if you like, I’m not headed into long explanations of he-said-they-said where the documents behind Humanae Vitae are concerned. Read the final product, it’s readable common sense that covers all you really need to know.
Here’s what I do want to say, though, about the opinions of theologians: Theologians are sometimes wrong.
The charism of infalliability is extremely limited. Basically it keeps the pope from royally screwing up when it especially matters most, and that’s about it.*
I like to think my theology is sound. I know for a fact that I fail spectacularly at many other tasks that ought to be wildly simple. I could really do with a secretary, a housekeeper, and a more vigorous conscience, thanks. That others have faults therefore comes as no surprise. So when you encounter something that seems like dubious reasoning even though it comes from someone who ought to know better . . . maybe it is, in fact, bad reasoning.
It is entirely consistent with history, doctrine, and a charitable disposition to consider the possibility an otherwise reputable theologian might, on some or many points, be haplessly incompetent.
It happens. Don’t stake your salvation on the smartness of mankind.
*Yes, infallibility also applies to the bishops teaching in union with the pope . . . which just brings us back to the important bit, which is that the Holy Spirit protects the pope from the very most disastrous errors.