Hmm... I'm not so sure this is a nitpick so much as a critique of my whole argument, but I'll try to tackle it piece by piece.

To begin with, as the West has secularized, I think we've seen a decreasing tendency to refer to Christendom as a unified object, but it's still a frequent trope at least in history texts. Furthermore, as a Jew myself, I do commonly see conversation, both in my community and outside it, about the movement of the Jewish world.

However, I will stipulate that obviously it's not heading in one direction. "Where the Islamic world is heading" is a discussion of broad trends in a community with common culture and common issues. And I would be doing a disservice to Naipaul if I suggested he meant anything more reductionist than that. Where I am critical of Naipaul, though, is that his projections of these broad trends are often wrong, the product of ineffective deductive reasoning from inadequate facts.

That doesn't change the fact that he paints of an evocative picture from an interesting perspective. If you haven't read the book, I would recommend it.