Here's my solution from another post:
What used to be "undocumented" is now considered "illegal". And from that, once made "legal" they are part of the system, either contributing to a growing corrupt government via forced taxes, or taking from it, which is also not acceptable.
If left "undocumented", the lady behind the government office counter will simply say "you don't have documentation, please step aside you're holding up the line".
"Undocumented" doesn't mean they don't pay taxes at all. Even if they are paid under the table, and/or live off the grid, whatever they buy in a store is taxed, which contributes to the local/state. Furthermore, if left "undocumented", they can not become citizens after 5 years. That's win-win for me and my pocketbook.