In the same way that the prisons have loads of people in them who never hurt anybody. How did those people get there? By not knowing the simple law that all they had to do was properly ask the court to bring forth someone that they injured. Rather, since they didn't understand how to ask this, they were talked into agreeing that they understood the legal code, and that they were guilty of breaking a legal code - which they didn't really understand - and many of them even signed on the line on some court paperwork thereby helping to incarcerate themselves.

If a person simply hires attorney, or if he accepts the attorney appointed by the courts, he is dooming himself to the mercy of the court, whatever they decide... just by accepting an attorney - https://www.youarelaw.org/Download/CorpusJurisSecundum-AttorneyClient.pdf.

What does this have to do with Trump and the wall? The wall might be totally justified to keep people out who shouldn't be here. But since almost nobody knows how to fight properly in court without an attorney, the courts can do anything to any accused, no matter what they are accused of. And the wall can wind up being an excuse to say that people are traveling to Mexico to avoid legal requirements on them in the USA, like medical requirements.

Certainly this won't happen right away. But it is a setting up of what will happen down the road in a decade or two, unless people wake up to their options regarding the courts.