I think people have all sorts of problems with immigration, legal or otherwise. There are those who mistakenly believe that immigrants take away their jobs, there are those who are merely nationalistic, and there are those (like me) who have nothing against immigrants themselves, but a great deal against the social programs that confiscate wealth for their benefit.
Then again, I don't like such social programs for bona fide American citizens, either. So, I guess that means I have no real issue with immigrants. As long as they're law abiding, and registered somewhere to ensure they're not terrorists, they're more than welcome.