Put simply: increased availability of contraception might lead to fewer pregnancies (the income effect) and to more people having sex (the substitution effect.) New Study Shows ’90s Era Condom Programs Increased Teen Fertility Rates. It's economics research out of Notre Dame.
The study is very rigorous. The authors identified 22 school districts in twelve states that launched condom-distribution programs during the 1990s. Some of these school districts are among the largest in the country including New York City, Los Angeles, and San Francisco. Overall, the study analyzes teen-fertility data from 396 high-population counties over a span of 19 years. A range of demographic and economic factors are held constant. It finds that if 100 percent of high-school students attended a school with a condom-distribution program, the teen-fertility rate would increase anywhere from 10 to 12 percent. Furthermore, this finding was fairly consistent across school districts with condom-distribution programs.Caffeinated Thoughts isn't surprised. "Twenty years of youth ministry experience tells me that free condoms led to increased sexual behavior." And the kiddie corps at Vox starts to grow up. "But it does call into question some of the unintentional side effects of making the contraceptive more freely available."
Bet on the side of the Law of Unintended Consequences. Plus sound economics.