How did this even become a case SCOTUS had to review? Did some judge somewhere, somehow rule that ILLEGAL ALIENS are exempt from US laws?
"Identity theft laws in most states make it a crime to misuse another person's identifying information – whether personal or financial."
"Because of the rise of identity theft and it's harmful consequences, Congress passed a law in 1998 making it a federal crime. Under the Identity Theft and Assumption Deterrence Act, it is a federal crime when a person "knowingly transfers or uses, without lawful authority, a means of identification of another person with the intent to commit, or to aid or abet, any unlawful activity that constitutes a violation of Federal law, or that constitutes a felony under any applicable State or local law."
This law was followed by the Theft Penalty Enhancement Act in 2004 which increased penalties for "aggravated" identity theft, requiring courts to impose additional sentences of two years for general offenses and 5 years for terrorism related offenses."
https://criminal.findlaw.com/criminal-charges/identity-theft.html