Less immigrants would negatively affect the GDP? I've heard the opposite many times, but I'm not an economist. Why is that so?
But the TLDR is: immigration brings skilled workers into the country, who produce more than they consume, raising GDP. So stopping the flow of immigrants causes GDP growth to slow.
Both because there is a lack of workforce in some areas (farms, low-end services) and because, in some countries where inequality is higher, part of the population feels these jobs are "bellow them" but somebody still needs to do them.
And last, even illegal immigrants contribute to move the economy. Everybody has to pay some level of taxes (even if only sales taxes) and has to consume goods. And illegals usually will try to "hide" and not use as much of public services.
I'm not advocating in favor of illegal immigrants. However, in my view, this is one of the main hypocritical reasons people in power complain about illegal immigration and, at the same time, don't do much to stop it nor to legalize those immigrants.
More people -> higher GDP.
I really dislike quoting the Bush administration on anything but here it goes:
http://georgewbush-whitehouse.archives.gov/cea/cea_immigrati...