That's part of it, but there are also "the law is the law" kinds of people, who perhaps don't realize how much more difficult it is for someone to move to the U

That's part of it, but there are also "the law is the law" kinds of people, who perhaps don't realize how much more difficult it is for someone to move to the US now than it was for their ancestors. I have no idea as to the percentages of both. There are also a lot of people who are victims of zero sum thinking and the lump of labor fallacy.