The Turkish "problem" is longstanding and kind on both sides as well. Many Turks are not that sure if they want to integrate into German society, and many Germans are not sure if they want them to either (though this sentiment is weaker than it once was). That produces a self-reinforcing situation.
Many of the current Turkish residents came during the 1960s as part of a guest-worker program [1], or are descended from those who did. The expectation was that they would be temporary workers (no path to citizenship) and eventually go home again. The program was closed in 1973, and the government spent much of the late '70s and '80s trying to encourage them to leave, more than encouraging them to integrate. There are many kids who've grown up 100% in Germany (some grandkids too) who aren't German citizens, and until very recently, were not encouraged to become citizens. (Germany does not have jus soli citizenship, and before a reform in 1999, it was also very difficult for someone not of German descent to naturalize.)
The fact that many Turks in Germany come from poor and highly conservative regions of Turkey (generally not Istanbul) doesn't help assimilation, of course. But it also doesn't help that the message for decades was that they aren't German and can't become German. And non-integration is complex, too. When Americans think of unintegrated Mexican immigrants, for example, they think first and foremost of Spanish speakers who can't speak English. But almost all the Turks considered unintegrated do speak German. Some (especially younger generations) don't even speak Turkish fluently (or at all), but only German.
Lots of these aren't German-specific problems, though. Since at least the late 19th century, European counties have been based on the ethnic nation-state, and transitioning to some idea that people can change nationalities, or even have more than one (and what that means) is slow and produces opposition.
As a Turk, I don't see the "Turkish problem" as being Germany's fault at all. These people went to Germany on a temporary basis, and decided to just not leave when the guest-worker program ended. In other words, they overstayed their welcome.
Imagine inviting a guest to your house for dinner, and them liking your house a lot and deciding to just move in permanently. Are you then expected to encourage them to put their name on the lease (i.e. become a citizen)? I don't think so.
If it were literally a 3-year temporary visa or something, I'd agree (and they wouldn't be there anymore, because overstaying would lead to deportation). But they didn't illegally overstay. They simply worked in Germany long enough to became German nationals. Partly, because in the EU (formerly European Community), the concept of a long-term "guest" with no rights is just not recognized: if someone lives in your country for years at your invitation, is able to support themselves and not engaged in criminality, and has learned some language/civics basics, they have a right to apply for permanent residency after some period.
I don't think I support the concept of a long-term "guest" with no rights, so I don't think it's wrong that such rights exist. That's what countries like Kuwait or Dubai do, with long-term "guest workers" who don't have legal rights. If someone has lived and worked here (Denmark) for 5 or 8 or 10 years or whatever, I think they should have legal rights on that basis. Much more so if they were born in Denmark; and doubly that if their parents were born in Denmark too, so that it's been two generations since they were immigrants. What is the alternative in that case, deport someone who was born and raised in Denmark to a country only their grandparents were actually from, and whose language they don't even speak?
Can you blame them? As I've heard it told, many of the German employers wanted to hold onto the employees they'd already poured training resources into (and enjoyed working with). Many of the Turks had established families and livelihoods in Germany by the time the guest worker program ended.
>As a Turk, I don't see the "Turkish problem" as being Germany's fault at all. These people went to Germany on a temporary basis, and decided to just not leave when the guest-worker program ended. In other words, they overstayed their welcome.*
Here's how it went down. First, Germany slaughtered and exterminated millions of people, invaded tons of countries, destroyed their infrastructure, commited heinous crimes, etc. What we know as World War II.
After the end of the war, West Germany, as a valueable ally of the West against USSR, got all kinds of help and special treatment to rebuilt its economy. And they started a program for bringing in workers from places they invaded and decimated, like Greece. Those workers, like the involuntary "arbeit mach frei" workers before, were brought to serve as cheap immigrant labor, under exploitative conditions, to assist the very people that had unprovoked invaded their countries and killed their relatives and fellow citizens a decade or so ago. The guest-workers, besides being exploited with lesser wages than Germans and fewer opportunities for advancment (like b-rate citizens) they were also treated with extreme racism and prejudice.
Now, the problem of the Germans (the "they overstayed their welcome") was that these people didn't just disperse when they were done with them, but instead felt that those hard working years in Germany gave them a right to stay and be integrated as full citizens.
I don't really understand this notion -- I usually get this kind of question from Americans: that if you consent to something, it makes it OK, regardless of the circumstances under which you gave your consent. I think this ideas usually comes from people playing life in "easy mode" (white, well educated, middle or upper middle class), that have never been forced to consent to humilliating or exploitative demands of the kind billions of people often have.
If I burn down your house (and kill your cousin and your Jew neighbors), and you or your kid, starving, accepts to come work for my company, and I treat you like shit on top, that doesn't make it OK in my book.
Many of the current Turkish residents came during the 1960s as part of a guest-worker program [1], or are descended from those who did. The expectation was that they would be temporary workers (no path to citizenship) and eventually go home again. The program was closed in 1973, and the government spent much of the late '70s and '80s trying to encourage them to leave, more than encouraging them to integrate. There are many kids who've grown up 100% in Germany (some grandkids too) who aren't German citizens, and until very recently, were not encouraged to become citizens. (Germany does not have jus soli citizenship, and before a reform in 1999, it was also very difficult for someone not of German descent to naturalize.)
The fact that many Turks in Germany come from poor and highly conservative regions of Turkey (generally not Istanbul) doesn't help assimilation, of course. But it also doesn't help that the message for decades was that they aren't German and can't become German. And non-integration is complex, too. When Americans think of unintegrated Mexican immigrants, for example, they think first and foremost of Spanish speakers who can't speak English. But almost all the Turks considered unintegrated do speak German. Some (especially younger generations) don't even speak Turkish fluently (or at all), but only German.
Lots of these aren't German-specific problems, though. Since at least the late 19th century, European counties have been based on the ethnic nation-state, and transitioning to some idea that people can change nationalities, or even have more than one (and what that means) is slow and produces opposition.
[1] https://en.wikipedia.org/wiki/Gastarbeiter