This book was written in an environment of multi-culturalism. To be against one or pro the other might offend the other. A multi-cultural society allows you to feel connected to different cultures, and culturally different points of view. Cultural differences are not of some one's own making but natural.
The importance of Christianity to culture is that, Christianity started social things like schools and hospitals, which are for the alleviation of the plight of society. Christianity involves things like our family lives and our personal hygiene, which are very important for our well-being. Christianity takes us as all equals in the eyes of God the Father, is not selfish but viewing every creation as important. How we view ourselves is how we should view others as important as ourselves.
Christianity is unique in that it combines many cultures. It started at the time of Jesus, which means those who came to Christianity, had their own cultures. Some cultures had to abandon what they valued before, such as polygamy, alcohol divorce, abortion and some rituals, which were anti-Christ. Some cultures were made to adopt some Christian cultures, which were not in their cultures before, such as Christmas and Easter holidays. With the fact that they were made to drop some of their traditions and adapt some Christian cultures could be the reason why they would start saying Christianity is killing culture.