The abortion rate has fallen again, to its lowest level since 1973, the year Roe vs. Wade was handed down. What's causing the decline? Should we be happy about it? Can we learn anything from it?

The answer to the first question isn't entirely clear. But the answers to the next two are "yes" and "yes." Pro-lifers are right that the decline is a good thing. And pro-choicers are right that what's causing the decline — and will keep it going, if we're smart — is women making these decisions on their own.

The numbers were reported Monday by two researchers from the Guttmacher Institute. They show a 13 percent drop in the abortion rate from 2008 to 2011, continuing a long-term decline that seemed to have stalled.

Some pro-lifers don't believe the numbers. But the National Right to Life Committee (NRLC) does, and it is happy to take credit for them. According to NRLC President Carol Tobias, the decline "shows that women are rejecting the idea of abortion as the answer to an unexpected pregnancy" and that "the long-term efforts of the right-to-life movement to educate the country about the humanity of the unborn child and to enact laws that help children and their mothers are having a tremendous impact."

Pro-choicers don't buy this spiel. They say the abortion rate is down thanks to contraception. Planned Parenthood points out that alongside the abortion decline, "births were also down," demonstrating "the importance of affordable, accessible birth control."

The best evidence for the pro-life theory is that, as the NRLC's Dave Andrusko points out, the abortion ratio — the percentage of non-miscarried pregnancies that were aborted — declined. That is, the percentage of pregnant women who chose to give birth increased. But this theory has problems. First, the decline in the abortion ratio was only half as big, in percentage terms, as the decline in the abortion rate. In other words, most of the decline in the number of abortions, relative to the overall number of women ages 15 to 44, was due to a reduction in pregnancies, not to pregnant women choosing life. In fact, the birthrate didn't increase. It fell by 9 percent.

Second, the laws don't match the abortion numbers geographically. As the Guttmacher report notes, "while most of the new laws [against abortion] were enacted in states in the Midwest and the South, abortion incidence declined in all regions. … [A] number of states that did not enact any new abortion restrictions and that are generally supportive of abortion rights … experienced declines."

The birth-control theory also has problems. The researchers concede that "little improvement in contraceptive nonuse among all women at risk of unintended pregnancy has been seen in recent years." But more narrowly, they observe: "Between 2007 and 2009, the level of nonuse among women younger than 30 decreased from 15% to 12% (a statistically significant change). In addition, substantial shifts in the contraceptive method mix away from less effective methods have been observed, particularly toward uptake of LARC" (long-acting, reversible contraception) methods, such as the IUD.

The report adds that from 2006 to 2010, "LARC use among women accessing publicly funded contraceptive services increased from 4% to 11%." During this time, "the estimated number of unintended pregnancies averted by federally funded family planning programs increased by 15% over this period (from 1.9 million to 2.2 million)." That's a big help — and a good reason for everyone to support these programs, not defund them.

The NRLC hasn't disputed birth control as a factor in the abortion decline. And why should it? You don't have to oppose contraception to oppose abortion. Instead, the NRLC defends pro-life education as a factor. The NRLC argues that disparities between states that passed pro-life laws and states that experienced abortion declines miss the larger cultural impact of these laws.

As Tobias put it: "The legislative efforts of the right-to-life movement, and significantly, the resulting national debate … should not be minimized. … The more Americans learn about the development of the unborn child and the tragedy of abortion, the more they reject abortion as a legitimate answer to an unexpected pregnancy."

What's striking about this argument is how indirect it is. By enacting legal restrictions in one state, you're affecting the moral convictions of women in other states. In philosophy, this concept, in simpler form, is known as legal moralism. It's the same logic often used to justify drug laws: Even if the laws don't work well or if they have serious unintended consequences, we need them to express and promote society's belief that drug abuse is bad.

Legal moralism is losing its grip on this country, and for good reason. People are becoming more sophisticated in their thinking about public policy. They want to know not just whether drugs, guns or abortions are unsavory or dangerous, but whether the law you're proposing would actually improve the situation. We have too much bad experience with prohibition.

If the strongest argument pro-lifers can make, in terms of their effect on the abortion rate, is that their moral message is persuading individual women, then why not focus more on that and less on legislation? Culturally, most pro-life bills are a waste of time.

There's no need to choose among contraception, choice and a culture of life. You can use birth control precisely because you don't want to risk an abortion. You can acknowledge the immorality of abortion, relative to pregnancy prevention, without abandoning the individual as the decisionmaker. Together, the cultural message and the technical means can drive down the abortion rate.

Everybody wins.