Basically to replace old people like you and expand the economy.
There are two basic ways to grow the economy:
(1) increase the number of workers and consumers; and
(2) increase worker productivity.
Item (2) covers technology, keeping people employed (no job, no productivity), overtime, etc.
Item (1) includes having children, young families (which consume a lot), and young workers.
The United States needs immigration to help with both. For example, because there are roughly 60 million stupid people in the Republican Party, many tech companies, life sciences firms, and universities are dependent on attracting highly educated foreign workers to fill their needs (e.g., my father, who arrived in the 1960s with an engineering degree).
In addition, with a rapidly aging population, we need immigration of young workers and their families to keep the population younger and to create more demand for consumer products (remember, 70% of economic growth is driven by consumer spending). The U.S. birth rate is too low without immigration to accomplish this.
If we reduce immigration, the U.S. will become a basket case like Japan ... with an aging population, shrinking work force, and workers who are burned out (because increasing worker productivity is the only way left for growing their economy).
Immigration grows the economy and creates jobs ... that is simply a fact.
Immigration is also essential for bringing in new ideas. Much of Silicon Valley has been led by immigrants or the children of immigrants.
The United States has thrived for over 200 years because of immigrants.
If you don’t understand that, then you don’t understand America.
DocBarrister