I think this is part of the equation about illegal immigrants which nobody in the US seem to talk about. They dont talk about all the companies exploiting illegal workers. We had a situation in Norway with exploited Polish workers. It was when Norwegian unions started targetting polish workers when things turned around. With polish info about workers rights, salaries and conditions improved. If you get unions more actively involved in the US you might not need big walls. Businesses are not going to hire mexicans if they cant pay them shitty salaries. If salaries and conditions are better americans are going to take those jobs instead.