Not really, the only thing you can't do with a green card is vote and citizenship is automatic (modulo paperwork) after five years. That, and you can get depor

Not really, the only thing you can't do with a green card is vote and citizenship is automatic (modulo paperwork) after five years. That, and you can get deported for a serious crime. But the status is naturally time limited. The second class citizens of the US are illegal immigrants. It would be trivial to get rid of them by cracking down on their employers but that would increase labor costs for their employers so the government turns a blind eye unless forced.