As well as the fact that they have no incentive to want to learn English since they have no legal status, and have no hope of being allowed to stay here since they know they can be deported at a moment's notice. People who are against normalizing their legal status should not be using Balkanization as a reason to oppose changing the status quo, since it is the status quo which is fostering this Balkanization.
Yes, you must have watched Threat Matrix last night....
They had a bit about that written into the show.