That comment is naive at best - do you really think that the majority of undocumented immigrants in the US can't find jobs? Why else would they be here, and why would their numbers dwindle during times of high unemployment?
If you really doubt that illegals can work in manufacturing, try googling for 'immigration bust factory', or similar stories.
If you really doubt that illegals can work in manufacturing, try googling for 'immigration bust factory', or similar stories.