The poll and title ask two different questions.
What percentage of people in the USA should be immigrants?
Economically, whether, within a given pool of laborers and proprietors, the individuals comprising that pool be or be not immigrants (legal) is irrelevant. To wit, as a former business owner, I cared about the citizenship status of sellers of labor I sought to buy is because the law required me to do so. Otherwise, however, I'd have been indifferent about that trait of a seller of labor (aka, a job applicant); I wanted a certain type of labor so I could achieve my business goals, namely delivering a particular set of services from my clients. I wanted excellent developers, project managers and analysts, not immigrant or non-immigrant developers, managers and analysts.
I'm sure folks can posit all sorts of reasons why the ratio of immigrant to non-immigrant buyers and sellers matters to them, but none of those reasons hold water on a macroeconomic level.
The best one can do to answer the question above is to identity an empirically coherent quantity at a point in time and convert that quantity to a percentage.
How many immigrants should we take in?
Whatever change in the quantity of authorized new immigrants that, in the
short run, allows the economy to operate at the limit of its
production possibilities curve.
With regard to the quantity of immigrants isn't something for which there is a constant figure. Sometimes the nation needs X-quantity of new immigrants and sometimes the nation needs a quantity other than X to achieve the same end.
Applying the Above Ideas to Government Policymaking:
To be clear, as goes governmental policy, what matters most to me is that the government enact policies that yield maximum economic efficiency. Such policies, in turn, function as the "rules of the game." Upon the rules of the game being published, it's then incumbent on the "players" to develop their skills and comprehension of them so as to, playing by the rules, maximize their personal utility.
Obviously, some people will be better absolute "players" of the "game" and others, in fact most, will be good players at one or another aspect of the "game." That's fine for so long as there is a way for everyone to obtain the maximum possible satisfaction that is possible given their relative investment in their playing ability, nobody, most especially native born citizens, has due cause to be dissatisfied. (One reaps what one sows, as it were.)
For example in the applied context of careers:
- Accounting careers have a range of lifetime earnings potentials. Other careers have greater and smaller ranges, as well as higher and lower range endpoints.
If what one wants to do professionally is accounting, one's delusional if one thinks one's going to become a billionaire merely by doing so. On the other hand, a career commenced in accounting (as an accountant) can lead to opportunities that may abet one's becoming a billionaire, or something close to it; however, one must have developed skills in addition to the accounting skills with which one started one's career.
So, if one's maximized one's potential as an accountant and one's yet dissatisfied (i.e., there remains unobtained utility that one nonetheless seeks), one must come to grips in one of the following ways:
[*=1]Expand the body of skills and abilities one has.
[*=1]Acknowledge that one chose a course that simply couldn't provide the utility one sought, and adjust one's utility expectations.
So it is with all careers. Even so, it's not, IMO, the government's role to do anything more than facilitate an environment that makes economic efficiency and
production maximization possible. Thus, if we need 10M immigrants because we haven't enough non-immigrants, we need 10M of them. If we need fewer, we need fewer, or if we need more, we need more. The quantity needed is what it is and it's empirically determinable.
