The key points:
"There is more than a little truth in Prothero's observations. Atheists are suddenly very hopeful about the secular trends and evangelicals are habitually prone to jeremiads about Christianity in cultural retreat. Nevertheless, there is more to this story than Prothero allows here."
"The real issue here is that I define Christianity in very different terms than those of either the ARIS study or Professor Prothero's minimalist use of the term."Another interesting point:
"when he [Prothero] discusses the 'Christian America' question in his classes, evangelical Christians describe America as a multicultural nation of religious diversity while non-Christian students see the nation as pervasively Christian."So America is "Christian", in the sense that our culture is still largely influenced by Christianity, rather than atheism or Islam. But this is "cultural Christianity". And largely inertia. Cultural Christianity is all about ignoring Biblical warnings: "that we may be no longer children, tossed to and fro and carried about with every wind of doctrine, by the sleight of men, in craftiness, after the wiles of error" Ephesians 4:14