Suppose you make cars safer by requiring seat belts, collapsible stearing columns, and other changes that make it less likely that an auto accident will kill the car's occupants. The obvious conclusion, and the one many people reach, is that the highway death rate will go down.
Sam Peltzman, in a classic article, pointed out that there was no good theoretical reason to expect that to happen. Auto accidents do not simply happen; they are the result of decisions made by drivers, such as how fast to drive, how much attention to pay to driving and how much to conversations with your passengers or listening to the radio, whether to drive home or take a cab after drinking a little too much. Making cars safer lowers the cost of dangerous driving; on the margin, drivers are more willing to risk accidents the less likely accidents are to kill them. So making cars safer results in fewer deaths per accident but more accidents. There is no theoretical basis to predict whether the net effect will be fewer deaths or more. Peltzman offered statistical evidence that, in the particular case he he was looking at—a collection of safety requirements imposed in the 1960's—the two effects roughly cancelled. Death rates per accident went down, the accident rate went up, and the annual death rate was about what it would have been without the changes.
I was reminded of this by a more recent controversy involving a different issue but the same logic. The Pope has, not surprisingly, come out against the distribution of condoms as a way of dealing with the AIDS epidemice in Africa—and, not surprisingly, been ferociously attacked for doing so.
Just as with auto safety and auto accidents, making sex safer has two effects working in opposite directions. It makes the chance that a given act of sex will result in AIDS transmission lower. But, by lowering that risk, it reduces the incentive to avoid sex entirely, to avoid sexual acts such as anal intercourse that are particularly likely to transmit AIDS, to avoid sex with people likely to give you AIDS, such as prostitutes. On theoretical grounds we have no way of knowing whether the net effect will be more AIDS or less.
It turns out that there is evidence that, just as in the auto case, the two effects roughly cancel. That, at least, was the widely reported conclusion of a Harvard AIDS researcher who had actually looked at the data. “We have found no consistent associations between condom use and lower HIV-infection rates, which, 25 years into the pandemic, we should be seeing if this intervention was working.”
All of which reminds me of another point, relevant to the Catholic church and contraception, which occurred to me quite a long time ago but which I don't think I have ever seen discussed. The church, for doctrinal reasons that are unclear to me, permits contraception via the rhythm method but condemns essentially all alternative methods. Critics of this policy frequently support their criticism with images of poor women who bear ten or twelve children, with terrible effects for themselves and, it is argued, the world.
The problem with that argument is that the particular problem they are concerned with is one—arguably almost the only one—that unreliable forms of contraception such as the rhythm method can solve. If your objective is to have four children instead of eight, a form of contraception that only occasionally fails will do a pretty good job of achieving it. That, presumably, is one reason why, prior to the invention of modern methods of contraception, birth rates responded to factors such as income that affected the desirability of having children, instead of being almost always near the biological maximum—although my guess is that the low tech methods being used were more likely to be coitus interruptus or oral sex than rhythm.
Unreliable forms of contraception can work pretty well for holding down marital birth rates. On the other hand, if your objective is to permit women to have sex with men they aren't married to without a significant risk of pregnancy—to permit, in other words, what has become the normal pattern of sexual behavior in developed societies—there is much to be said for more reliable forms of contraception.
Which leads me to suspect that neither side of that controversy is being entirely honest about its objectives. The Catholic church defends its position on doctrinal grounds, but it can be interpreted, perhaps more plausibly, as social engineering. Limiting contraception to unreliable methods—rhythm, which the church approves of, and interruptus, which it has no way of preventing—makes casual sex considerably riskier without imposing large burdens on marital sex and thus makes the former less attractive as a substitute for the latter. Critics of the church's position claim that their concern is with overpopulation and poverty, but support contraceptive technologies that enable—arguably have created—the modern pattern of sex largely outside of long term relationships.
On general principles, of course, I think contraception should be legal. On the question of whether improved contraception has had, on net, good or bad effects I am agnostic; I can see legitimate arguments in both directions. My point in this post, however, is not to support either side of that question but only to point out reasons to suspect that neither side of the controversy over contraception is being entirely honest about its motives.
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