Jonathan Klick (a co-author of mine) and Thomas Stratmann (a colleague at GMU) have written an interesting paper on abortion and risky sex among teenagers. From their conclusion:
Incentives matter. They matter even in activities as primal as sex, and they matter even among teenagers, who are conventionally thought to be relatively myopic. If the expected costs of risky sex are raised, teens will substitute toward less risky activities such as protected sex or abstinence. In addition to modeling the decision making processes of teenagers, this insight is important in other contexts as well. Many public policies can be improved by recognizing the sensitivity of teenage sexual decisions to costs and benefits.
We study one set of policies in this paper. We show that increasing the cost of abortion for teens lowers the insurance value of abortion. This induces teenage girls to avoid risky sex, which will likely have the effect of lowering pregnancy rates, abortion rates, and birth rates among this group of individuals. While these positive effects alone might not justify parental involvement laws, they presumably should not be ignored in the debate. Behavior is not static, and claims based on the assumption of static behavior are flawed.