“... build what are in effect prisons, ... on the north side of the border with Mexico. ... called customs holding centers, ... under customs authority. So US federal judges cannot interfere with them.”
This part Sounds very good!
“It is indeed a very bad idea to just “kick them across the border”, because they will either immediately join one of the drug cartels, or be murdered by them as an enemy. And this can come back to bite us later.”
And why should we care what becomes of native mexican criminals? They need to be Mexico’s problem and locked up or killed within their own country. Mexico doesn’t want them? too bad.
Because the drug cartels are large, violent, and more than willing to cross the border with military style weapons to attack Americans. So trickling their criminals back to them is an awful lot more cost effective than stationing two or more US Army divisions on the border.