Germany will take unlimited numbers of the flood of refugees from the Middle East and North Africa, after all. Germany will welcome 800,000 refugees this year into in a population of 80 million.

The German welcome is stunning given the bitter history. This generation cannot be blamed for the murder of its own Jews, or those the Nazi generation dispatched to the death camps from the countries the German army occupied. But the experience with German guest workers of the 1960s and ’70s, who contributed to the enormous German prosperity, was not a happy one, either. The German government assumed that these workers, mostly Turks, would remain for only two years. But when the agreement ended in 1973 most them stayed, where there were jobs, little unemployment and generous welfare benefits were readily available.

By 2010, there were 10 million Turkish-speaking residents, many children of the original immigrants, poorly educated in German, and were usually not citizens. Germany, like most European nations, uses “the right of blood,” rather than place of birth, as in the United States, to grant citizenship. Christian sponsorship of German schools, growing Islamic revivalism, women’s rights and the wearing of a headscarf as a symbol of the veil, all complicated the problem of becoming “German.”

Now Germany proposes to absorb increasing numbers of Arabs and black Africans, with the bitter example of French “no-go ghettoes” close at hand. The changing German mood, as illustrated by Frau Merkel’s example, is a puzzle. One persuasive argument for expanding the population, though rarely discussed except in economic terms, is Germany’s sharply declining birth rate. Niklas Potrafke, of the prestigious Ifo Institute, argues that Germany should spend this year’s budget surplus of $7.8 to $10 billion on refugees. Holger Schmieding, an economist at Berenberg Bank, agrees. “If Germany gets this right,” he says, “it may just be solving part of its demographic problem for the next decade.

Demographics is a serious obstacle to continued German prosperity. By 2060 there will be fewer than two Germans under 65 to work and generate taxes to support each German over 65. Age-related spending on pensions, health and long-term care is expected to rise a hefty 5 percentage points of national income by 2060.

Taking in large numbers of young men who may not share nor want to learn German values and traditions is a gamble. Governance itself might be threatened in the future. A melting pot is difficult when refugees and other immigrants don’t want to melt.