well, i didn't had read yet the whole trhead but there is a thing i mostly see with illegal immigrant people
not always an illegal immigrant get free pass to get in US again once its done with turist visa expiration, at least here in Brazil our visa is valid for 5 years, and it seems an bilateral treaty will increase this peiod for 10 years, the point is: its deffinatelly hard to get an Visa here even for me an medium citzen who has no pretentions to live in US, its quite hard to get an student/tourist visa, i can't imagine a person who need to worlk offshore to survive, like an low class citzen to get an opportunity to evolve in US, this situation in Brazil, when i think it is one of richest and have very good relations with the US in latin america, i can't figure how this could work with an Mexican , Peruvian, Bolivian or else, that's for sure quite harder to get a visa, its a dellicated situation and IMO, treat such people with bad conditions just because they don't have legal cover in american soil, its quite coward.
not all officers treaty people bad, some even help those peoples but , the major treatment with illegal, its not far, IMO.