When Carol Baltosiewich was a Catholic nun, she spent 10 years caring for young men dying from AIDS. Even so, the first time I spoke to her, in 2016, I was terrified to tell her I’m gay. As a reporter who covers the church, I had started interviewing Catholics who worked and fought during the height of the H.I.V. crisis in the United States, roughly 1982 to 1996. People like Ms. Baltosiewich persisted amid frequent hostility from church leaders toward gay people and the broader stigmas of the time. A poll in 1987 found that 43 percent of Americans agreed...