I forgot to mention that the demographics in Germany that Stefan cited are even worse when you look at young-aged people.

Even before the refugee crisis we had 36% migrants (people with "Migrationshintergrund") among the children up to 5 years. This number is from 2011.

You can see this pretty clearly in the population pyramid with highlighted "Migrationshintergrund":

The green and the saturated orange in the middle represent the migrant population. Note that this population pyramid is from 2014 and thus also does not include the refugees yet...

Around 2030 the people in the large babyboomer section will become pensioners. It is hard to imagine how the german pension system is supposed to survive this. 25% (around 80-90 billion EUROs) of the federal budget are already dedicated to supporting the pension system today, year for year.

The German welfare state will not survive a lot longer.