For Cristina Hineman, the situation felt urgent: the 17-year-old needed treatment at Planned Parenthood, where she knew she wouldn’t be subjected to humiliating questions, or an unnecessary waiting period, or lectures, or prying about her certainty. But it wasn’t an abortion she sought. It was testosterone. Planned Parenthood was founded a century ago to promote birth control. Today, its nearly 600 clinics nationwide make it the largest single provider of abortion, contraception, reproductive care, and sex education in the U.S. It has also, in less than a decade, become the country’s leading provider of gender transition hormones for young adults,...