Pope Paul VI

"Whatever is opposed to life itself, such as any type of murder, genocide, abortion, euthanasia, or willful self-destruction, whatever violates the integrity of the human person, such as mutilation, torments inflicted on body or mind, attempts to coerce the will itself; whatever insults human dignity, such as subhuman living conditions, arbitrary imprisonment, deportation, slavery, prostitution, the selling of women and children; as well as disgraceful working conditions, where people are treated as mere instruments of gain rather than as free and responsible persons; all these things and others like them are infamies indeed. They poison human society, and they do more harm to those who practice them than to those who suffer from the injury. Moreover, they are a supreme dishonor to the Creator".

Pastoral Constitution on the Church in the Modern World Gaudium et Spes, 27