Does it have to go beyond failure of historical memory?

I'd been wondering for a while why the reaction to Muslim immigration has been so much more brazenly bigoted in famously liberal northern Europe than in the United States. Not that we don't have our problems, but our politicians are at least better at couching their concerns in euphemism. 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.