Matthew Yglesias writes:

The problem of teen/single/unwed motherhood is one of the relatively few issues liberals and conservatives seem to be able to agree on these days. The right is more likely to pitch the issue in terms of marital status (“single moms”) and the left in terms of simple age (“teen moms”), but both sides reach the same basic conclusion. Raising a child is difficult. Raising a child without help from a partner is very difficult. Doing it at an early age is going to substantially disrupt one’s educational or economic life at a critical moment, with potentially devastating consequences for one’s lifetime. Therefore, preventing early nonmarital pregnancies (whether through liberal doses of contraception and sex education, or the conservative prescription of abstinence cheerleading) would seem universally desirable.  

But perhaps we’re approaching the problem from the wrong direction, according to Melissa Kearney and Phillip Levine in a new paper “Why is the Teen Birth Rate in the United States So High and Why Does It Matter?” published in the spring issue of the Journal of Economic Perspectives.  

They conclude that “being on a low economic trajectory in life leads many teenage girls to have children while they are young and unmarried and that poor outcomes seen later in life (relative to teens who do not have children) are simply the continuation of the original low economic trajectory.” In other words, it is a mistake to the leap from the observation that women who gave birth as teenagers are poor to the view that they’re poor because they gave birth. Lexus owners are much richer than the average American, but that doesn’t mean the average person can get ahead by buying a Lexus. Women with better economic opportunities tend to do a good job of avoiding childbirth.

Sure, but the bigger question is: What's in society's long-term interest? I mean, where do the next generation of poor children come from? Does the stork bring them?

Obviously, with the exception of immigration, poor children are mostly the product of poor parents.

Society is better off if the kind of young women whose lives wouldn't be ruined by having a child out of wedlock reproduce less rapidily. 

Let's take a real example: black teen illegitimate fertility spiked up during the Crack Era, peaking in 1991. Various thing happened after that that reduced it, probably including welfare reform and FDA approval of long term contraceptive shots for girls.

Black teen fertility has been significantly lower since 1991. You never, ever hear about that historically important trend, though, because A. You aren't supposed to say that having fewer poor black teens around today than if 1991 had gone on forever is a good thing (What kind of depraved Nazi eugenicist are you?); but, B. Everybody with a brain in their head thinks it is a good thing.