Illegal Industrial Reserve Army?

Marx found that through out history there was always an industrial reserve army that helped to keep wages low. This army came in the form of slaves and serfs. Without this group people would have continued to demand higher and higher wages in Marx's view. In class, we decided that today's industrial reserve army is illegal immigrants.

So in the view of some, illegal immigrants are actually helpful to us by their effect on wages but I'm sure that those who have to lower the rate they would usually work for so that they can get a job over an illegal would disagree. It's obviously wrong for an employer to a give a job to some one in the country illegally just to cut costs but many do. It is pitiful that so many citizens are out of work while so many here illegally hold jobs.

My question is "Are the illegal immigrants necessary to our economy by forming this industrial reserve army? Could we have a legal one?" I honestly don't think that many citizens would be willing to work for the wages illegals are for obvious reason. But there are those who while they wouldn't not for dirt-cheap they would work for lower wages than most and do it legally. So I think we could have a legal industrial reserve army. they are just over shadowed by illegal immigrants.