You say "[a] country filled with Arabs, Africans, and Afghans isn't Germany" and then question someone who wants to preserve their child's Israeli and Austrian heritage.
Trying to use genetic heritage to determine nationality is an unproductive use of one's time. You would be right in saying that the native populations of South Germany and Austria are similar genetically, but native North Germans are more similar genetically to the Dutch, Danish, and Swedish. Perhaps you also argue for those nationalities to identify as German?
I wrote the preceding sentences before checking your comment history (and remembering the neo-Nazi reference of your username). Now that I have, I can see why you would have a problem with non-Caucasians identifying as German and German parents wanting their children to remember their non-German heritage.