Let me ask you something, seriously:
Let's say they pass this guest worker thing, what if 50% don't sign up and find ways to get around it so they can still work for cash to send and wire home. Will you favor deporting them in that instance if they refuse to sign up for the plan?
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.