ZZ:
In the 19th and early 20th century, America wanted additional population to build an expanding nation. There was a need for unskilled labor to work hard in our sweatshops and factories. Not the case today.
The Irish (Catholics) were certainly discriminated against by the Yankee, established Protestants. It took a couple of generations for immigrant Irish to be integrated into our society. We have not had similar success in advancing a great many black Americans.
I should think we'd want to take care of our own before bringing in a zillion immigrants from every god-foresaken nation on earth.