Children born with ambiguous genitalia were often operated on to form one gender or the other. While this wasn't for a biological reason, the rationale was just

Children born with ambiguous genitalia were often operated on to form one gender or the other. While this wasn't for a biological reason, the rationale was justified by social science. There are issues that arise from children not identifying with 99% of the population, and physicians and parents sought to avoid that. It turns out that it might be at least as problematic to choose "incorrectly" for your child.