Does it have to go beyond failure of historical memory?

I don't require it to: it's sad enough on its own. I'm just not certain if more specific issues are in play, and I'm not sure I'm sleeping enough to articulate the questions that might elicit them.

Then, while reading The Jews of Medieval Western Christendom, it occurred to me that that part of the world didn't experience any significant non-Christian immigration between the Middle Ages and the past few decades.

I hadn't even considered that as a factor. I suppose when your most recent template for cultural interaction is the Ninth Crusade . . . Good grief.