Excellent article in the Atlantic Monthly.
Author Derek Thompson
This is a complex problem. Coming to America is good for most immigrants - they receive more income. If they don't do well they return to their home country.
It is good for the world economy - people immigrate to where they can earn higher wages then at home. If and when they return home they return with more money and skills that can help their local economy.
It is also good for our US general economy - More workers means lower wages.
But extensive immigration of low skilled workers is bad for our own low skilled workers - more competition for less skilled work means lower wages. This in turn increases social problems, increasing crime rates and welfare costs.
It seems to me that we must regain control of our borders, and limit the number of low skilled folks we let enter our country. And we should probably have a guest worker program where we let immigrants enter our country for a few years, then to return to their country of origin.