1. The presumed law would be easy to comply with, and scofflaws need to go home.
2. Avoiding registration means that they want to avoid compliance with tax law ( a felony) or that they have a criminal record (also a felony).
3. Non-compliance could also mean that they weren't here for work but rather crime of some sort or terrorism.
I think this is what is missing from te current debate. I think many conservatives, including myself, would go along with this if those refusing to signup were deported and kept out for good.
Most of us have a problem with people who piss on us, make demands, and try to convince us that we are racists for not wanting to continue the chaos and looting.
I think we need people who want to be Americans first and foremost, not Mexicans who simply want to come here, exploit the situation, and still hold their blood oath allegiance to Mexico.