It was a Words with Friends chat that first gave Megan Phelps-Roper pause. Along with much of her family, Phelps-Roper belonged to the infamous Westboro Baptist Church, a cult-like sect that spreads hateful messages about gay and transgender people. But in online conversations with her Words with Friends opponent, C.G., Phelps-Roper began to see the church through his eyes and recognize its cruelty, which led to still more questioning. “Little by little,” she wrote in her memoir, Unfollow...