We Americans ought to have the right to presume that government is doing its job. One of its jobs — in a fundamental sense, one of its primary jobs — is to keep our borders secure. That's part of "providing for the common defense." We ought to be able to presume that anyone walking around on the streets of our towns has the right to be there, and that anyone presenting themselves for work in our shops has the right to do so. Absent some reason to be suspicious of that person's status, we ought not to have to do government's job of ferreting out illegal foreigners. Absent some reason to overcome that presumption, we ought not to have to check their immigration or citizenship status, any more than we ought to be checking to make sure that drivers have licenses to operate a vehicle.
That's just part of being a free society, even if other people don't like it.