"... they undercut the wages in any given area to the detriment of the community at large..."
Bingo! That's the whole point of bringing them here, isn't it? Not only do you get to exploit them, you get to indirectly lower everyone else's wages, too.
But wait, there's more! The money they send home to their families is removed from the American economy, they simultaneously get to contribute to our tax rolls and and put a strain on our welfare system. And best of all, they're so scared of losing their jobs and getting deported they'll put up with any crap we dish out to them.