Immigration policy has to be derived from more fundamental principles.
Both the United States and the Earth have unsustainable populations. They are unsustainable with present technologies, and they will become dramatically unsustainable once petroleum production comes off its peak.
We need an objective study of what would be a sustainable long term population in the United States. Then we need reproduction and immigration policies that get us there.
While we are waiting for that, as an intermediate measure, we should adopt an population-neutral immigration/emigration policy. That is, for every person immigrating into the country, we would want to see an emigrant. If an American senior retires to Mexico, for instance, then a young Mexican worker would be allowed to legally enter the United States.
I would also be open to negotiating labor treaties with countries so that workers would be cross-employable. This has already been done in the European Union. Then, for instance, if we had such a treaty with Mexico, any Mexican could live or work in the U.S., whose citizens would have reciprocal rights in Mexico.
When the laws of the United States are brought into line with its real needs, then I would support severe measures against anyone (or any business) that encourages illegal immigration.