Whether someone has a green card (the proper documentation in the immigration context) is a completely different question than whether someone possesses the requisite skill set to perform a job.

I believe the 11 million number represents an average of estimates of TOTAL illegals here in the US. The actual number of workers is probably about half that number.

As to serious harm to the economy..it depends – if they walk out and go home, there are some corresponding cost savings that accrue but at worst, I believe it would just be a disruption as wages would rise to fill the positions or we would decide that we could do without certain services if they were only available at too high a cost.

Finally:

“…that we don’t normally think of as illegal – that is, the activity of work itself (when that work is performed without proper documentation).”

The legal profession has so many barriers to entry that any conclusion we come to in these forums has the advantage of being strictly academic. Because, of course, many of us would be outraged if some schlub started practicing law without going through the requisite schooling and testing – you know, without proper documentation….and if law schools ever threaten to fill their faculty from outside of those with the proper documentation of Law review-published, Ivy-educated and certifiably diversity-conscious – well, I’m sure we’ll then be inundated with thoughtful pieces on the value of a properly documented workforce.