Two years ago in June 2010 Thilo Sarrazin, former member of the Executive Board of the Deutsche Bundesbank, argued that especially Muslim immigrants are strongly connected with claims on the welfare state and crime. Moreover he stated that in no other religion the transition to violence, dictatorship and terrorism is so fluid. It sparked a national debate with a lot of public figures denouncing Sarrazin but some people, especially through internet forums etc. supported him and his statements. Whatever one's opinion about him might be, he sparked an important debate about immigration. The following articles (from Spiegel) show what should be considered when talking about immigration.
"Study Hints that Mutual Suspicion is Slowing Integration"
"Germany Needs More Foreigners"