Most Turks in Germany are citizens (requirements are if anything laxer than in the US), and there's practically no religious extremism among Turks, so that's just a wrong claim.

And actually extremism among Turks is absent for the very reason I outlined above. In Turkey there's a long tradition of either religious integration in the state in the Ottoman era which had a strong scholastic tradition, or laicism under Atatürk, so there was very little room for sectarianism.

And yes, a lot of extremism is present among refugees, but that just proves the point, where do refugees originate from? Countries with failing state authority.