This issue is complex. What the Mehmet case illustrates is that the right offers up a symbolic solution (extradition) which it can't carry through. For instance, you can't deport a young Greek because he's an EU citizen, and you can't deport a young Turk who lives in Germany because of a treaty, signed at the EU level. It conflicts with EU law, it conflicts with the European Convention on Human Rights, and it probably also conflicts with the German Verfassung. So, it's never going to hold up, but yet the right keeps pounding its symbolic drumbeat of deportations. Purely for electoral purposes, in this case.

The issue is indeed complex; therefore, I don't believe it can be reduced entirely to Right-versus-Left terms, though there is that element to it as well as an "election campaign drumbeat"at the present time. It's certainly true that laws against deportation from Germany have been tightened in recent years, but close inspection reveals that in each new decision there are caveats allowing deportation after consideration of strict criteria applied to a particular case.

The Mehmet affair in Munich is a case touted as a purely Right-Left controversy; however, there were ordinary people of every political stripe in the Bavarian capital who applauded the deportation of Muhlis Ari, the young Turk's real name, and they regretted the Bavarian court decision allowing him to return to Munich. The case genuinely alarmed those who were concerned about violence and crime involving youngsters. Many a voice could be heard in Munich saying, "We have no choice but to deal with our own German offenders, but let's deport foreign citizens, who are not our responsibility." That widespread reaction in Munich is a fact, and there's no getting round it.

You wrote:

What I did find out in the mean while is that there is a large amount of debate among criminologists about which approach will work and that I am largely unqualified to comment upon it. If you have the time to read the wiki article on zero tolerance, you will find that it is (in some parts) written from a POV that is outright hostile to that approach.

German media over the years have reported visits of American officials invited to Munich to explain their success at home with zero tolerance. One such American was quoted in the German press as saying: "Why do you Germans put up all your signs banning this or that when you don't enforce the ban? What then is the good of a smoking ban on public transportation or a ban against riding a bicycle the wrong way in a one-way street?"  The Americans advocated strict enforcement of every single ban. Otherwise, they said, don't put up the signs.