They come here to work/increase productivities. If they come here to take benefit and not work that is bad. But this is different.
A Town will expand economic wise when they can get people to move in. People who will work to excel and to have a better life.
They have to eat and buy stuff, they pay taxes: sales taxes. They don't pay fed taxes but they also don't get social security money or a lot of other benefit. This is why they get paid under the table and the low rate.
Would you rather have a lot of 1) American citizen who are so redneck and unproductive, lazy and on wellfair OR 2) Mexicans who work hard to make a better life? I would choose the second choice. This is because they will expand the economic base in where they live.