There is this Pizza place in my town that I often go to. It's owned by this older Italian guy and his daughter. They have a number of Mexican employees who work there. Now when the old Italian guy is there, the Pizzeria runs horribly. He yells at kids, has a hard time keeping track of who pays and who doesn't. He is always confused, screwing up orders, the kitchen looks like it is a mad house. His daughter is just mean and treats the customers very poorly and doesn't show any respect for someone like me who has been there hundreds of times before. She thinks I would do something like walk out with paying, and really creates a hassle. Now when the owners aren't there, the Mexican guys run the place like clockwork. They are always very friendly, on top of things, treat the customers well. It brings such a smile to my face when I walk in there and don't see either the owner or his daughter because I know I am going to have a plesant dining expierence.
Now this is just an anecdote and both the Mexicans and the old Italian guys are probably immigrants, but most pople would say the Italian guy was American before the Mexicans. They may be here illegally, they may not speak the best English (although neither does the old Italian guy), they are almost certianly forced to work long hours, probably aren't very well educated (at least here in the US), get paid poorly and under the table. It just always amazes me they are able to run the pizzeria so much better then the owner. If only the old guy would stay home, the place would be so much better.
Around here, Mexicans line up at the train station as day laborers. They get picked up by contractors or whoever, get paid like $100 to do some meinal job. They have to work all day, don't have any insurance or anything like that. But they are just trying to work hard and provide for their family. They want their kids to have an easier time then they did. And to be honest, someone in society needs to fill those sort of jobs. And if its immigrants who are willing to do whatever just to get a foot in the door, then good for them. There isn't any shame at all in that. And yes, some of them don't try to assimilate or anything, don't learn the language, live off welfare and unemployment or whatever. However I know a lot of "real Americans" that do that too, if not moreso.