The poster also refers to the Freakonomics theory that the decline in criminality is caused by the legalization of abortion. While this is an appealing theory, in many ways, the numbers are at best ambiguous. If I recall correctly, another explanation that has better numbers to support it is the reduction in lead in the environment, which happens at approximately the same time as the legalization of abortion. Moreover, it more handily explains local variation. Communities saw crime reduction commensurate with the amount of lead abatement done in that community.