Do the abortion math

It’s the thirty-fifth anniversary of the famous Supreme Court decision in Roe v. Wade that affirmed the legality of abortion.

Of course abortion remains a fantastically polarizing subject. It seems like the country is divided fairly evenly in favor of choice and opposed to it (and not necessarily along traditional party or ideological lines); and that most opinions are strongly held.

I for one believe that Bill Clinton got it exactly right when he said that abortion should be “safe, legal, and rare,” but why do I believe that? No opinion is worth having if it can’t be examined, challenged, and defended, so here is my defense.

First we must determine whether it’s possible to attack or defend abortion dispassionately, without appeal to emotion. Most people who oppose abortion do so because they believe that it is murder, a naturally emotional subject. We could try to remove or distort the emotional component (e.g., by confining ourselves to a discussion of costs and benefits — as routinely happens in cases of state-sponsored murder such as executions and wars), but I think there’s another way that sidesteps the question of murder altogether.

Whether or not abortion is murder depends on whether or not a life exists to terminate. Indeed that’s what it came down to in the Roe v. Wade decision:

We need not resolve the difficult question of when life begins. When those trained in the respective disciplines of medicine, philosophy, and theology are unable to arrive at any consensus, the judiciary, at this point in the development of man’s knowledge, is not in a position to speculate as to the answer.

Nearly everyone agrees that life does not exist prior to conception. Nearly everyone agrees that life does exist upon birth. So where, in between those two events, is the switch flipped? We don’t need medicine, philosophy, or theology to decide; just simple math.

Life may not exist the entire time, but what does exist is an ever-increasing probability of life — more precisely, a probability of being born alive. The appearance of a fetal heartbeat at about eight weeks after conception improves the odds. “Viability” (a minimal ability to survive outside the womb) at about 22 weeks improves it some more. The chances of being born alive continue slowly to climb as the fetus develops, until finally it reaches 100% at the moment the baby takes its first breath.

Can we scientifically choose a probability threshold before which we say abortion is OK and after which we say it isn’t? Sort of. A threshold very close to 100% would be unacceptable to most people, even pro-choice advocates, for emotional reasons (although this has not been true at all times or in all cultures, some of which routinely disposed of unwanted infants simply by exposing them to the elements). It makes no sense to talk about a threshold of 0% as some extreme anti-abortionists might prefer it, because the probability is higher than zero even before conception — especially if Barry White is playing and the lights are turned low. Any other choice between 0% and 100% would be arbitrary, so the best we can do is to choose the least arbitrary number in that interval: 50%. As it happens, in modern America a 50% chance of a live birth appears to be reached, on average, between the 22nd and 28th week of pregnancy.

So that’s my position: abortion should be legal (and safe and rare) before about 22 weeks, and illegal (with the usual pragmatic exceptions — rape, incest, health of the mother) otherwise. Your emotions aside, I think I’ve shown that no other position on this subject is more rational than that one.

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