Immigration opponents often point to the precipitous drop in the share of Europe's population that identifies as Christian – from 66.3 percent in the early 20th century to 25.9 percent in 2010 – which they blame partly on the combination of high immigration from Muslim-majority countries and declining birth rates among native Europeans.

In 2030, Muslims are projected to make up just 8 percent of Europe's population.

In any case, immigrants to Europe aren't all Muslim.

Add to that religious shifts among "native" Europeans, with many choosing not to attend church or identify as religious, and it seems clear that claims about immigrants diluting Christianity in Europe are not rooted in reality.

Of course, immigration opponents might argue that the threat to Europe is not so much a matter of official religion as of the values, cultivated in Europe's Christian societies, that underpin liberal democratic institutions.

Even immigrants who come from countries with autocratic governments and problematic cultural norms are, once in Europe, held to the same legal standard as Europeans.

Nonetheless, these immigrants, Europe's right-wing politicians declare, could still bring religious fundamentalism with them, threatening Europeans with the terrorism that is tearing apart their home countries.

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