Border control
The U.S. is a large nation with extensive borders, and there are a lot of reasons other than economic that controlling unauthorized entry and exit is a good idea.
150 years ago they were Irish and Chinese, then they were Italians, then they were Jews from Eastern Europe... after WWII, they were Catholics from Eastern Europe. Now they come from Central and South America, and speak Spanish. So what?
It's a little bit different now. As just one example, I don't recall demands for ballots, schooling, signs, and government documents to be in Chinese or Eastern European back then.