One of the oft-cited arguments against allowing increased immigration is that all those immigrants will take jobs away from Americans. In the abstract, that's a somewhat misguided point. Immigration growth is very similar to having rapid population growth because of higher birthratesboth increase the number of working-age people in the United Statesand we rarely hear calls for people to have fewer kids on the theory that all those youngsters will "take our jobs away." There isn't a fixed number of work in this country, and population growth meansagain, in theorymore jobs for everyone.
Anyway, Mark Thoma has more on this point, and there's a good debate in his comments section (including people that don't agree that the two are exactly the same) that's very much worth reading.