First off, are you saying that because you believe it or just to play devil's advocate?
I agree that immigrants are vital to our country. My mom is a first generation immigrant. If she didn't come here I wouldn't exist. I'm not asking that they give up all their traditions and cultures. If you want to celebrate Kwanza, Ramadan or Hanukkah, all the power to you, but don't expect the entire country to follow suit. Tolerance is different than promotion.
I do expect that immigrants speak at least one of our national languages, it's necessary in order to communicate and to be a useful and productive citizen. And don't even get me started on those who come here just to live off of our social assistance programs. (I know it's not just immigrants that abuse the system, but I have a problem with anyone who does)
The trouble is that so many people identify as Polish, or German or Chinese or whatever, (even those born HERE!) that they are slowly eating away at our national identity. To feel more patriotism about a country other than the one you are a citizen of could cause real problems in the future.