Actually, they're not. We have a very generous policy for ME immigrants. We cut back after 9/11, but now the Saudis and other ME folk have obviously worked their magic, and we are letting in lots of non-Christian ME people, either on temporary visas (which of course they will overstay) or on a family reunion basis. I'm not worried about Mexicans; I'm really worried about Muslims, but nobody seems to care about restricting their immigration to the US.
Plus, of course, Muslims come backed by Saudi money. I was in Houston last week and saw that the "Islamic Dawa [Conversion] Center" has bought an old courthouse downtown next to the new TX State Court.
"Actually, they're not. We have a very generous policy for ME immigrants."
Our immigration policy, as bad as it is, does tend to be employment and skills based. So the people coming here legally tend not to be the dregs of the earth. Even the illegals have to go through a fair amount- fly over to Mexico, hire a coyote, etc. Plus, those who just want to collect welfare would obviously try to emigrate to Europe, not here.