As much as I hate to say it, Jimmy Akin is in error on this point.
“[E]very action which, whether in anticipation of the conjugal act, or in its accomplishment, or in the development of its natural consequences, proposes, whether as an end or as a means, to render procreation impossible” is intrinsically evil [CCC 2370].
I’ve boldfaced the phrase “conjugal act” because it’s the key to understand what is being said. Many gloss over this phrase and assume it means “sexual act.” It doesn’t. “Conjugal”—like its Latin equivalent, coniugale—doesn’t mean “sexual”; it means “marital.”
If you are having sex with someone you are (heterosexually) married to then you are engaging in the marital act. Otherwise, not. If you are engaging in sexual behavior but not with someone you’re married to then it is a different kind of act (masturbation, adultery, fornication, etc.).
What the Church—in Humanae Vitae and the Catechism—has done is say that one cannot deliberately frustrate the procreative aspect of sexual intercourse between man and wife....
And so it’s left the field [of sex outside of marriage] largely to moral theologians to discuss and not really treated it on the Magisterial level.
While it is true that the 20th century Magisterial pronouncements on contraception all discuss the "conjugal act," it is NOT the case that this phrasing is only meant to reference the sexual act within marriage.
For precedence, we have the Fathers and Doctors of the Church, who clearly forbid the use of contraceptives regardless of the marital state of the participants.
Consider, Aquinas for instance, whose Summa was enshrined with the Scriptures on the altar at the Council of Trent. He had no compunctions about discussing the relative merits of sex outside of marriage, going even so far as to grade the various levels of damnation that masturbation, fornication and bestiality inflict upon those who practice such vices (he judged fornication the least damnable, since it was at least ordered towards the conjugal act, lacking only the vow of marriage for liceity - for his complete discussion, click here.)
Indeed, several Fathers specifically mention infidelity as a reason participants indulge in contraception and abortion, and those contraceptive/abortifacient extra-marital acts are still specifically and explicitly forbidden:
"[Christian women with male concubines], on account of their prominent ancestry and great property, the so-called faithful want no children from slaves or lowborn commoners, [so] they use drugs of sterility or bind themselves tightly in order to expel a fetus which has already been engendered" (Refutation of All Heresies 9:12 [A.D. 225]). ~ Hippolytus
"For necessary sexual intercourse for begetting [children] is alone worthy of marriage. But that which goes beyond this necessity no longer follows reason but lust. And yet it pertains to the character of marriage . . . to yield it to the partner lest by fornication the other sin damnably [through adultery]. . . . [T]hey [must] not turn away from them the mercy of God . . . by changing the natural use into that which is against nature, which is more damnable when it is done in the case of husband or wife. For, whereas that natural use, when it pass beyond the compact of marriage, that is, beyond the necessity of begetting [children], is pardonable in the case of a wife, damnable in the case of a harlot; that which is against nature is execrable when done in the case of a harlot, but more execrable in the case of a wife. Of so great power is the ordinance of the Creator, and the order of creation, that . . . when the man shall wish to use a body part of the wife not allowed for this purpose [orally or anally consummated sex], the wife is more shameful, if she suffer it to take place in her own case, than if in the case of another woman" (The Good of Marriage 11–12 [A.D. 401]). ~ Augustine
"Why do you sow where the field is eager to destroy the fruit, where there are medicines of sterility [oral contraceptives], where there is murder before birth? You do not even let a harlot remain only a harlot, but you make her a murderess as well. . . . Indeed, it is something worse than murder, and I do not know what to call it; for she does not kill what is formed but prevents its formation. What then? Do you condemn the gift of God and fight with his [natural] laws? . . . Yet such turpitude . . . the matter still seems indifferent to many men—even to many men having wives. In this indifference of the married men there is greater evil filth; for then poisons are prepared, not against the womb of a prostitute, but against your injured wife. Against her are these innumerable tricks" (Homilies on Romans 24 [A.D. 391]). ~ John Chrysostom
"Who is he who cannot warn that no woman may take a potion so that she is unable to conceive or condemns in herself the nature which God willed to be fecund? As often as she could have conceived or given birth, of that many homicides she will be held guilty, and, unless she undergoes suitable penance, she will be damned by eternal death in hell. If a woman does not wish to have children, let her enter into a religious agreement with her husband; for chastity is the sole sterility of a Christian woman" (Sermons 1:12 [A.D. 522]). ~Caesarius of ArlesNow, these are all good quotes, but the next one is the real kicker:
"I am supposing, then, although you are not lying [with your wife] for the sake of procreating offspring, you are not for the sake of lust obstructing their procreation by an evil prayer or an evil deed. Those who do this, although they are called husband and wife, are not; nor do they retain any reality of marriage, but with a respectable name cover a shame. Sometimes this lustful cruelty, or cruel lust, comes to this, that they even procure poisons of sterility. . . . Assuredly if both husband and wife are like this, they are not married, and if they were like this from the beginning they come together not joined in matrimony but in seduction. If both are not like this, I dare to say that either the wife is in a fashion the harlot of her husband or he is an adulterer with his own wife" (Marriage and Concupiscence 1:15:17 [A.D. 419]). ~ AugustineIn fact, according to both Augustine and all subsequent Catholic doctrine, no contraceptive act can be conjugal because the very contraceptive act itself breaks the marriage compact and is therefore done outside of marriage. That is, even married people who contracept are not participating in "the conjugal act" because the act of contraception renders the sexual act non-conjugal.
Note that Augustine's reasoning is exactly parallel to the idea that the Bride of Christ, the Church, is sinless. How does She manage that, given that each individual Christian is a sinner? This is possible because when any one of us sin, the sinner is no longer part of the Body of Christ. We need to go to confession in order to be made sinless and be re-united to the sinless Body.
So, in light of Augustine's insights, if we take Jimmy Akin's understanding as correct, none of the Magisterial documents actually discuss contraception, since all of them concern themselves only with the conjugal act, and contraception renders the act non-conjugal or extra-conjugal.
This is obviously an absurd conclusion.
Akin's reasoning must be wrong.
So, what is meant by "conjugal act"?
In order to reconcile the writings of the Fathers with the Magisterial documents which base themselves on the Fathers, we must assume that "conjugal act" does not strictly confine itself to meaning "the sexual act that takes place within marriage", rather, it must mean "the sexual act that is supposed to take place within marriage (but often does not)".
Have we any precedent for such a referencing?
As a matter of fact, we do.
When we meet someone like George H.W. Bush, Bill Clinton, or George W. Bush, we refer to each of them as "Mr. President." Why do we do that? After all, none of them is president anymore. Yes, none is president, but all three once held that office, so in order to honor that memory of them, we refer to them as "Mr. President" even though they are not properly in office anymore. They were once elected to that office, and that fact must be honored.
In Magisterial documents such as Scripture, we see St. Paul do the same thing when he calls the members of various communities "saints" - he calls them what they are striving to be, not what they are right now. He uses the language of perfection (that which will be perfected), not the language of imperfection, when referring to holy things and holy people. He refers to them by the office they will one day, through God's grace, hold, the office they are elected to hold - that's why they are called "the elect."
In the same way, the "conjugal act" is a holy act, a holy office, and it deserves honor. So, the Church in her documents always refers to the sexual act as the act that is proper to marriage: whenever possible, She calls it "the conjugal act." Indeed, in order to honor its holiness, it is called that even when we are actually (or also) referencing the sexual act outside of marriage, precisely because that act properly belongs only in the sacred office of marriage.
So, Pope Benedict's private theological opinion on the matter of condom use is not unusual in addressing the question of the relative merits of different kinds of sex outside of marriage. Augustine, Hippolytus, Aquinas, and numerous others constantly did the same. This is not exactly a new problem.
Similarly, saying that one kind of act may not be as bad as another kind of act, yet both acts may still damn you to hell, is also not a new habit for private theologians, whether that private theologian be the Pope (in this instance) or Aquinas. After all, it was just eight hundred years ago that Aquinas pointed out how someone who chose fornication over masturbation has chosen a less damnable (albeit still damning) sin, because fornication at least involves a real person and a real possibility of procreation, while masturbation is just an illusory pleasure-taking.
In order to find precedent for Benedict's private theological speculations, we need not make up examples about bank robbers or muggers. Such examples have nothing to do with marriage or the marriage act or the violation of the holy institution of marriage. They really don't apply.
We need only go back and examine the writings of the Fathers and Doctors of the Church, comparing their examples to the examples set before us today.
So, is the Holy Father's private theological opinion correct? Is it the case that the use of the condom with the intent to reduce disease transmission less damnable than using the condom without that intention? Probably. Aquinas, whose love for such fine distinctions is precisely what makes him the greatest doctor of the Church, would almost certainly agree that it was.
And that is heartening.