BS, "they won't survive the training"
US citizens aren't incompetent and illegal Third Worlders aren't some magical crowd of hard-working geniuses....some are great workers, some are lazy, some are stupid, some are intelligent
People are people....
If you actually believe that there aren't competent US citizens who could roof, or work on houses, or do whatever, you are simply fulfilling self-fulfilling prophecy of not hiring them.
If a plant wants to hire illegal immigrants illegally as cheap labor, that's on them, they also should be fined and prosecuted.
There are several companies (even big ones) in the US that specifically are trying to get H-1 visa help from India and won't even try to openly hire any US citizens, because they know they can pay them so cheap, it makes them millions more...
It's not the US citizen's fault they want slave labor and can't or won't pay decent rates
Also funny how illegals are only hired in force in 3-4 main occupations, I worked in two very large industries as both a training/hiring position and as an executive manager and I have never ever hired an illegal immigrant, and only had one apply in 25 plus years