I think people are missing a major factor in this situation. Visiting relatives who come here legally to visit could be at risk for incarceration, at least temporarily, since the would not be able to provide proof of legal residency. They could have this happen for something as simple as a traffic violation (it's legal to drive on a foreign DL while visiting the US).
And I know the response will be that they should carry their passport with them at all times (since that is th eonly way they can prove they are hear legally), but that is not a good idea at all. While you do need identiifcation of some sort, your passport should be kept secure. You can get home without your ID, but not without your passport. And it's a bitch to get a replacement passport while travelling abroad.
I would not want to risk that my family members from abroad would undergo such treatement while they come to visit me (which happens very often).I would choos eto move away from Illinois if they passed such laws, and I'm a born-citizen.