We have several generations in our society who live in almost complete ignorance of the true history of Christianity. They have absorbed so many false memes from an anti-Christian popular culture that they believe them without even thinking about them. They think, for example, that it was the church that brought on the so-called "dark ages". In fact, the so-called "dark ages", i. e. the medieval period after the fall of the Roman Empire, were brought on by non-Christian hordes from the North who invaded and physically destroyed Rome. The keepers of the intellectual flame during the medieval period were, largely, church related institutions, including monasteries and the Vatican. Oxford University's motto reflects its religious origins.
The anti-Christian left is, in truth, against all religion, but it attacks Christianity first and foremost because Christianity is the world's largest religion. Leftists claim to be moral relativists, but really, what that means, is no morality at all. What is moral, to a relativist, is that which benefits him or her most. So killing a baby is okay because it makes the mother feel better. The baby might inconvenience the mother. Old people might inconvenience younger people so kill them.