Many years ago I attended a conference organized by a national Catholic organization on the topics of marriage and human sexuality. One of the speakers was a professor from Creighton University who, in the middle of his talk on contraception, launched into a long tangent about how the Church had never condemned slavery in the past, which “proved” that the Church had made a mistake, and so perhaps its teaching on contraception would be viewed as incorrect in the future (a viewpoint he agreed with).
I did not get the opportunity at the conference to talk with this professor about his erroneous statements about the Church and slavery, so I emailed him and we engaged in a courteous exchange in which I pointed him in the direction of several papal condemnations of slavery, which he dismissed out of hand. He ignored the historical record because it did not fit with his agenda of changing Church teaching on contraception.