I had a friend who argued against objective morality citing the following regarding canabalism. How do I respond to this?
Morals vary dramatically across time and place. One group’s good can be another group’s evil. Consider cannibalism, which has been practiced by groups in every part of the world. Anthropologist Peggy Reeves Sanday found evidence for cannibalism in 34% of cultures in one cross-historical sample. Or consider blood sports, such as those practiced in Roman amphitheaters, in which thousands of excited fans watched as human beings engaged in mortal combat. Killing for pleasure has also been documented among headhunting cultures, in which decapitation was sometimes pursued as a recreational activity. Many societies have also practiced extreme forms of public torture and execution, as was the case in Europe before the 18th century. And there are cultures that engage in painful forms of body modification, such as scarification, genital infibulation, or footbinding – a practice that lasted in China for 1,000 years and involved the deliberate and excruciating crippling of young girls. Variation in attitudes towards violence is paralleled by variation in attitudes towards sex and marriage. When studying culturally independent societies, anthropologists have found that over 80% permit polygamy. Arranged marriage is also common, and some cultures marry off girls while they are still pubescent or even younger. In parts of Ethiopia, half the girls are married before their 15th birthday.