Well, duh, that is precisely the point, Justice Breyer.
Breyer said the Arizona law upsets a balance in federal law between dissuading employers from hiring illegal workers and ensuring that people are not discriminated against because they may speak with an accent or look like they might be immigrants.
Total leftist garbage and Breyer should be ashamed of himself for making such a stupid statement, but I'm sure he isn't. But any citizen of the US, and any legal resident, has documents readily available or obtainable to prove their eligibility to work in the US. (And any few who don't can obtain such documents with reasonable effort.)
The federal government mandates the US of E-Verfiy for its contracts. I wonder if Breyer is aware of that. Lamar Smith is sponsoring legislation to make E-Verify mandatory nationally. Failing that, the states will enact their own mandatory E-Verify legislation like AZ.