About demographics and Mark Steyn's statistics, going on here.
For me, it boils down to "What are the rates?" The disparity can't be reconciled here, and Steve gave an example of the Palestinian Authority grossly inflating its fertility rates for the UN stats. And it is a given, across cultures, that fertility rates have depressed with the onset of industrialization. So it's UN v. CIA--who's more reliable, and why?
Finally, let me reiterate that America Alone has a broader thesis, too--the radicalization of Islam by petrodollar-powered Wahhabism (the Saudi "Burka King franchise," to use Steyn's memorable phrase), the enervating effects of multi-culti thinking and welfare/nanny-statism in the West, and related items. But inaccurate stats gut the rest of the book.
Keep it going--it's an important topic.