I was brought up to believe that morality is about objective facts. Just as snow is white, so also infanticide is wrong. But attitudes vary with time and place. The norms that I was taught are the norms of my own society; other societies have different ones. Morality is a cultural construct. Just as societies create different styles of food and clothing, so too they create different moral codes. I've learned about these in my anthropology class and experienced them as an exchange student in Mexico.