I hesitate to use the "It's for your own good" argument: However poorly paid, poorly housed, and poorly treated immigrants are, they're still likely to view themselves as better off than they were. And I'd grant more weight to the idea that having emigration to the US serving as an escape valve that reduces the pressure for improvement at home, if the places they were coming from had working political systems that would allow for change driven by democratic pressure.

Really, that's what needs to be fixed: If the countries that are producing net immigration to the US had political systems and economies that worked, the immigration problem would fix itself. But it's the sort of thing that can't really be fixed by the US. The one thing that we can do that might help—allowing people to visit the US to attend school, make business contacts, and so on—is also the thing that makes it impossible to reduce immigration without using police-state tactics. And having a police state is a solution that's worse than the problem.