The New Atheists’ historical account of religion is far more dubious. Christopher Hitchens says that religion is merely implicated in everything bad, while Harris attempts to establish a direct causation. These arguments are historically slanted. Dawkins, meanwhile, often berates religious “Bronze Age myths” that hold civilization back. That’s not even the right age!
A sketch of a more realistic view: human beings have constantly fought and killed each other from our earliest days, and we developed various religious forms as societies became more complex. Scholars such as Francis Fukuyama argue that mass religions were a key factor in the development of the modern state, because they allowed the creation of mutual-aid networks much larger than tribal societies based on descent from a common ancestor.
Religion did not invent crusading violence nor racism, though it has eagerly participated in both. It is a part of the deeply flawed human experience, partly good and partly bad.