I would agree with you except that Christianity is not monolithic. In fact, if you want to set it up like a tree, with Christians stemming from Jews, then Catholics stemmed from Christians, and protestants stemmed from Catholics, so today's Christians are far removed from the Christians of the Bible. Mormons historically stemmed from protestantism, although the claim is they are really a restoration of the early Biblical Christians. So when someone says they are a "Christian" what do they mean? Early Bible Christian? Cathoilc? Protestant? Eastern Orthodox? Evangelical? Trinitarian? Gnostic? They all are Christians, and yet their doctrines are not all the same. Even if you lump them together with trinitarianism, there are Christians who are left out, and that isn't the original premise. It isn't based on doctrinal distinctions, but on who "really" believes in Jesus, just as who "really' believes in the God of Abraham, Isaac and Jacob (vs. Abraham Essau and Mohomed). But, even Muslims believe in Abraham as a prophet, in essentially the same way we do. God was just a lot more violent then.