http://www.weeklystandard.com/blogs/chamber-ceo-us-needs-more-low-skill-immigration-americans-are-not-qualified-or-willing-do-such-work_781624.html
Motivation? Make a bigger pool of structurally unemployed workers and then apply the boot to lower wages.
I have no problem with them coming over here. The economic effects, I am unsure of. I think if we are going to have immigration laws like we do, then we do have to enforce them, however.