The notion that banning illegal immigrants would cause the economy to collapse is ridiculous. We don't depend on them for the progression of our economy. They are mearly filling jobs that others would fill if they weren't there. It's frustrating when people try to make a case for allowing illegals to stay by saying that we can't function without them.
That said.. I'm all for immigrants coming and finding work, paying taxes, and contributing to society. I don't care where they are coming from, or what jobs they are seeking. Globalization is a good thing, and this is part of it. These workers do assist is trade specialization.
Of course our economy would be strong without them. It is also strong with them. So it isn't a matter of economy collapse if they were banned. It is a question of how the economy will change. The way I see it, the major impact is that of inflation and the value of the U.S. dollar. Those who step up and fill the jobs that illegals leave behind might initially want to be paid more for the same work. If they do indeed recieve higher pay then inflation jumps. The big question is whether legal citizens will work for the same pay.
In any case, the economy will adjust regardless and the worst that would happen is a relatively short period of either higher inflation or higher number of "poor" families.