I've seen migrant agriculture workers packed into cell-sized shanties with barely any utilities, and kept under slave-like order. Not on the Mexican border, but in the Pacific Northwest. I was looking in 1995, but we could also try some research on migrant conditions. For example:http://www.migrant.net/pdf/farmworkerfacts.pdf
As for the conditions in domestic labor, some chapters of Ehrenreich and Hochschild, Global Woman
(Holt Paperbacks 2004). Women often pressed into long hours with ambiguous or no contracts, kept isolated from others of their language group, frequently humiliated if not sexually abused, sometimes beaten, sometimes kept hidden, papers taken... This saves people and government a whole lot of money. It makes time for some middle and upper class women to stay there, and often provides for their children's care. All of this while distancing mothers from their own children in less wealthy countries.
There is a question as to how many established citizens would choose low-paying, uncomfortable, high-risk jobs that migrants often do. Many would certainly bristle at the conditions being imposed, which are below legal. Or, some are excused as being "beyond the purview" -- they are not citizens, not legal etc. Tough luck.
There is systemic exploitation of migrants precisely because they are generally not
citizens. This serves to keep the prices of produce and domestic service low. It's similar to buying textiles at Walmart (but Walmart is just one particularly strong example) because labor and overhead are cheaper in Asia. Industries and/or government which do not provide across the board
for the security, health and welfare of many laborers are cutting a very meaningful profit.