At the same time, it's not a bad time to say something about the Catholic position on birth control. It is probably the ethical position most at odds with the modern utilitarian view of morality, and it makes no sense if you don't understand the central principle of Catholic ethics in general.
The central principle of Catholic ethics is that it is teleological. If you don't get this, then most Catholic ethical positions will make no sense at all.
There are basically three kinds of ethical systems. The first is consequentialist: an action is right if it produces good effects. Utilitarianism is the most widely known kind of consequentialism. The second is deontological: an action is right if the intension is to act in accordance with ethical rules. Immanuel Kant's ethics is considered a paradigm case of deontological ethics.
The third school of ethical thought, that to which Catholics are at least supposed to adhere, is teleological. What does it mean to say that Catholic ethics is "teleological"? The word comes from the Greek word telos, meaning, roughly, "purpose." This is widely known today as "virtue ethics," a view of human actions that is based on an Aristotelian-Thomistic view of reality. In modern times this view has been championed most notably by G.E.M. Anscombe and Alasdair MacIntyre. In fact, MacIntyre's book After Virtue is one of the most important and influential philosophy books to have come out in the last 50 years, and is almost single-handedly responsible for the contemporary revival of virtue ethics.
MacIntyre makes the case that, since the rejection of the Aristotelian-Thomist worldview during the so-called Enlightenment, teleological ethics has largely been abandoned in favor of various consequentialist and deontological views of ethics that have largely failed for a variety of reasons. And this, in turn, is the result of the rejection of two of Aristotle's four cases: formal cause, which the intrinsic pattern inherent in every thing, and final cause, which is the inherent purpose (telos) in every thing, and is aligned implicitly in each thing to that things formal cause.
The only coherent system of ethics, MacIntyre argues, is teleological.
Ethics in the teleological view is very simple. There are men as we find them in the world and men as they would be if they fulfilled their telos. Ethics is the best way to get from the first to the second.
Furthermore, because formal and final causation are rational concepts, virtue ethics yields a rational ethical system, one which short-circuits the fact/value distinction that plagues every other ethical system. There is no fact/value distinction in Catholic ethics, since ethics is itself a rational system.
Catholic ethics then, being teleological, is based on purpose. But more specifically, it is based on the intrinsic purpose in natural things, most importantly in man. If you look at the list of Catholic ethical positions, it will make sense only if you understand this.
This is particularly evident in sexual ethics. In Catholicism, a sexual act, like any other act, is judged right or wrong according the telos implicit in the act. The telos of the sexual act is reproduction. If the sexual act is performed in conflict with this purpose, or if the purpose the act is somehow interfered with, then it is wrong.
This is why the Catholic Church is opposed to contraceptives: They interfere with the intrinsic purpose of the sexual act.
Now as soon as you say this, you get rhetorically jumped by people who either don't understand teleological ethics or don't agree with it. They either argue that reproduction is not the only purpose of the sexual act or that no act has any intrinsic purpose and that the purpose of any act is whatever the doer has in mind.
As to the first kind of response, the usual argument is that pleasure is obviously a purpose of sex, and therefore reproduction is not the only purpose. But the argument that reproduction is not the only purpose of the sexual act is irrelevant, since it is not the position of the Catholic Church that it is. The Catholic position is that reproduction is the primary purpose and other purposes are subordinate to it.
It is also irrelevant because the argument confuses the natural purpose of a thing and it's extrinsic, human purpose. As Catholic philosopher Edward Feser has put it:
It is also irrelevant that people might indulge in sex for all sorts of reasons other than procreation, for I am not talking about what our purposes are, but what nature's purposes are, again in the Aristotelian sense of final causality. Now it is true of course that sexual relations are also naturally pleasurable. But giving pleasure is not the final cause or natural end of sex; rather, sexual pleasure has as its own final cause the getting of people to engage in sexual relations, so that they will procreate.In other words, of course there are other purposes to sex than procreation, but they themselves only serve to enhance the primary purpose.
Then, as we said, there is the argument of those who don't think anything has any intrinsic purpose at all. This is the real objection, and, in fact, the people who argue that sex has some purpose other than procreation really don't believe in intrinsic purposes at all, anyway, even though they sometimes talk as if they do.
If you take this position--and reject all formal and final causes in nature--then you are left with the position that the heart is not for pumping blood, and the kidney is not for filtering the blood, and teeth are not for chewing, and the brain is not for controlling the rest of the body.
Just be glad doctors don't believe this--or at least that they don't act as if they did.
Under this view, nothing, in fact, is for anything.
And if you take this position, you are, of course, in the strange predicament of saying that the reproductive organs are not for reproduction.
It's not a position I would want to defend.