Re: Who started this ?
Except illegal labor isn't just about farm workers. I also know people that have done some of that work. To claim that NO ONE would do it otherwise is a little disengenious. The farmers would just have to pay real wages and costs would increase (the same as paying "living wages" to burger flippers).
Although that's not the end of it. Illegals have been pushed in other industries (like meat packing) helping to drive down working conditions. When you lot get hysterical about American chicken over at the Guardian, labor abuse is part of that picture.
I also have relatives that have been meat packers. So you can't say that job wouldn't ever be done by "white as sour cream" Americans. The same goes for construction.
The real problem is that the illegal labor pool creates an underclass ripe for exploitation and helps drive down labor standards for everyone.