Immigration and Assimilation

Since talking about minorities would get me labelled a racist, I'll talk about part of my own ethnicity, the Germans. If a German wanted to become an American, he or she must assimilate into our culture. Some say "But their culture would be lost!!" Oh really? No more Germany? Cause that is where their culture is and that is where their culture will stay. Their culture won't change, they will. How is them changing a bad thing?