Do this all started as a failed German Experiment? Not for nothing, these Germans had millions of WWII refugees floating around, had just killed off millions of people for racist and other stupid reasons, and they choose Turks? What the F is wrong with these Germans! Maybe it is God's punishment for that whole Holocaust writ large (jews, poles, gays, handicapped) thing.
They chose Turks for a simple reason: 30 million German men had simply dissappeared (i.e. died)in the war. The nation was then divided by the victorious Allies, and labor (non Nazi labor. Remember, there was a vicious de-nazification process in the 1940's and 50's) was in a such short supply that even with the Marshall Plan and the acceptance of West Germany into NATO, there simply were not anouth people to do the work needed to put Germany back on it's feet.
So, they turned to an almost bottomless reserve of unskilled labor in the Middle East, which had mostly remained untouched by the war, and of whom, it could be reasonably expected, all would go home after their contracts ended. Unfortuntely, the 70's dawned and with it a whole host of touchy-feely, multi-culti philosophies regarding explotation, human rights, etc.
However, German industry became just as addicted to cheap labor as American industry is. Muslim immigration only became a major issue (rather than an acciptable annoyance) after the reunification of Germany (there were now East Germans who needed jobs, you know). But how do you reconcile the German need to be seen as "sensitive" (after their Nazi past) with the economic and political realties of today?
That's the heart of the issue. And it's an issue all over Europe. The Europeans have avoided answering it, and so, have planted the seeds of their own eventual demise because to do what is necessary is bad for the soul (not to mention public relations).
Western Culture is being destroyed from within by outsiders and their fellow-travelers on the political/academic left. Time to take out the trash, folks.