Here is an example of why hiring illegal aliens is not economically productive for the United States. Try to follow along.
You have two families: "Joe Legal" and "Jose Illegal". Both families have two parents, two children, and live in California.
Joe Legal works in construction, has a Social Security Number nd makes $25.00 per hour with taxes deducted. Jose Illegal also works in construction, has NO Social Security Number, and gets paid $15.00 cash "under the table". Ready? Now pay attention...