The word “heartless” gets thrown around a lot at times like this. But it is not heartless to note that taking in huge waves of migrants from the Middle East has come with problems, particularly for Europeans. Even President Obama has acknowledged that Muslims have had a hard time assimilating in Europe.

There is no shortage of evidence that Arab and North African migration comes with challenges. That includes rioting in French banlieues, the Charlie Hebdo attacks, and the fact that many of the 9/11 hijackers lived in Germany, and that nearly half of all violent crimes there are committed by foreign-born youths.

Also, as we’ve seen time and again, even when mass migration is relatively painless, telling citizens that it is illegitimate and bigoted to want less of it inevitably leads to a backlash.

When demand outstrips supply — and turning to market mechanisms isn’t an option — all that is left is rationing.