>>Like it or not, the migrants aren’t planning anything illegal.<<
Wrong. The second they step foot on U.S. soil without explicit authorization based on personal identification, passport documents, etc., they have perpetrated an illegal act and are subject to detainment and/or arrest.
Nonsense.
If they request asylum they are entitled to a hearing under US law.
Those hearings take place on US soil and if history serves as a guide most will be released with a notice to appear at a later date. All perfectly legal.
When they don't show up for their hearings they'll lose their temporary legal status.