America is talking about teen pregnancy. Britney Spears's baby sister Jamie Lynn, all of 16, is pregnant. The father, her 19-year-old boyfriend Casey Alridge, who may or may not face statutory rape charges for having sex with a minor, is someone she met at church. Then there is Juno, a satirical comedy about a tortured but well-meaning 16-year-old who gets pregnant and decides to give her baby to a childless couple who later want to divorce. It has been fascinating to watch the debate sparked by these two moms-to-be, with the principal question in each scenario being, "Why didn't she...