"Some in the German blogosphere have speculated about Selen's ideological background. What is known is that throughout his government career, Selen has been resolute in confronting Islamic fundamentalists in Germany. He also led BfV efforts to monitor the Turkish nationalist Milli Görüs (Turkish for "National Vision"), an influential Islamist movement strongly opposed to Muslim integration into European society."
A lot of Muslim in Europe, before the Syrian refugee crisis, despise Islamic extremism. That's why the went to Europe in the first place. His appointment does in fact serve Merkel's political needs, but his career makes him look like a solid pick aganist Islamic terrorism.
You forgot to mention...
According to the posted essay, Erdogan urged Merkel to appoint Selen.
In other words, only those opposed to Erdogan, who now is the most powerful person in Germany.