Immigration again

One of the major arguments immigration proponents use is that we are a nation of immigrants and all of us are descended from immigrants so what if they wanted to wall off the borders before your forefathers came? This is an apples to oranges argument. For most of us, our ancestoral immigrants came to the Americas in the eighteenth or nineteenth centuries. The U.S. was mostly a vacant land needing bodies to fill it, to farm it, to man the new plants that were going up everywhere. That was then. Now, the country is full. No new lands to discover. No new farms to plow. As far as the manufacturing plants go, is it merely a coincidence that the first public discourse and discontent on immigrant occurred in the 1920s when unemployment became real and personal? When companies were begging people to take jobs and immigrants could not do so quickly enough, that was find. But now jobs are still scarce . . . the imaginary 5% unemployment rate does not take into account those discouraged that they have stopped looking or the underemployed . . . if it were to do so, the rate would be closer to 10 percent or higher.
The other argument used is that immigrants only take jobs Americans do not want to do. Let us paraphrase it correctly: Immigrants only take jobs Americans do not want to hold AT THE RATE OF PAY OFFERED. Research has indicated immigrants pull down the wages for a community since they are willing to work for much lower than regular Americans. Companies are smart and offer less with fewer benefits. But recent stories about ICE raids and companies needing to fill these positions have indicated a surge of American citizens applying for those jobs. So nix that argument too.
Companies should offer jobs to American citizens and pay a liveable wage before offering jobs to aliens. (If your regular citizen has a mortgage and pays utilities, he or she naturally needs more to live on than a mexican alien living twelve to a house)
Companies have a responsiblity to American citizens. They want to hire americans to get American productivity and creativity and know-how but want to pay Indian wages with Chinese health/safety/labor benefits. They cannot have it both ways.