It would be good to look at our past for a similar situation:
Benjamin Franklin, in his 1751 pamphlet Observations Concerning the Increase of Mankind, wrote:
"Why should the ... [Germans] be suffered to swarm into our Settlements, and by herding together establish their Language and Manners to the Exclusion of ours? Why should Pennsylvania, founded by the English, become a Colony of Aliens, who will shortly be so numerous as to Germanize us instead of our Anglifying them, and will never adopt our Languages or Customs, any more than they can acquire our Complexion."
...Pennsylvania was at this time about 33% German immigrants....
Last time I was in Pennsylvania they spoke English. Of course, I do too, but then I'm a descendent of those folks he was talking about.
1. Ben was wrong, the Germans learned English.
2. Every other immigrant group has learned. Most of them the children of the immigrants, immigrants themselves tend to be poor and older and don't learn the language, or don't learn it well, But their children do.
3. EVERY immigrant group that has come to America has done it, Chinese, Japanese, Mexican, Norwegian, German, Italian...
4. THe immigrant bashers are wrong, English language and American culture will thrive on new immigrants who will in a generation be as completely American as I am.