Catholic philosophers and theologians who support Rome's position on "artificial" birth control attempt to construct natural law arguments in defense of that position. And pop Catholic apologists recycle those arguments.
Natural law arguments can be valuable, but they need to be formulated with great finesse. Teleology, per se, isn't sacrosanct. There's nothing wrong with impeding gravity so that we can fly airplanes. Likewise, water pumps contravene gravity to make water flow uphill.
The natural goal of a chicken egg is to hatch into a chicken, but it's not immoral to violate its tells by consuming scrambled eggs. Eating veal parmesan disrupts the natural order. After all, calves were designed to grow into cows or bulls. But eating veal parmesan is not immoral–the protestations of vegans notwithstanding.
The nose and ears weren't designed to be a platform for glasses, but it's okay to co-opt them for that purpose.
If letting nature take its course was a general (much less universal) imperative, that would pretty much abolish the medical profession.
The point of counterexamples is to test whether you consistently apply the principle you appeal to, or whether you make ad hoc exceptions.
The standard Catholic argument against "artificial" contraception treats procreation as a special case of a general principle: natural teleology. The question, then, is whether the general principle is sufficiently discriminating to justify that particular application–while compartmentalizing that application from other permissible examples that run counter to the ordinary course of nature.
(When I say "special", I'm not using "special" as a synonym for "exceptional"; rather, I'm using "special" as a synonym for "specific"–in contrast to generic. For instance, brain cancer is a special case of cancer. Cancer is the general category, of which brain cancer is one example.)
The question is why the other examples, which interfere with the ordinary course of nature are permissible, but "artificial" contraception is not.
The Catholic argument begins with the general principle of natural teleology, then treats procreation as a special case of that principle. And it regards the natural teleology as normative with respect to human procreation.
Problem is, Catholics are forced to admit that natural teleology is not a reliable indicator of normative ethics. There are ever so many cases where it's permissible to disrupt the natural order. Take pesticides. Or selective breeding.
Or, to consider some examples involving human pregnancy, viz. epidural anesthesia during labor and delivery. A caesarian section? Those artificially circumvent or contravene the ordinary course of nature.
What criteria can Catholics use to refine their appeal to natural teleology while preserving their appeal to natural teleology. They can't begin with that principle, then admit that it may properly be superseded in any number of cases. In that case they have no consistent operating principle.