Ultimately this comes down to ignorance and fear.  Who are these people crossing the border?  Are they Americans?  Are they migrants?  Are they refugees?  What law applies here?  I know that they're crossing illegally because if they tried to cross at border crossings, they'd be turned back.  Beyond that, I don't know how the law should be applied, and based on many of the comments here, I'm guessing most people don't know either. Certainly the politicians don't know.

Perhaps if someone had a good idea on how to deal with these people that actually fell within the law and our international agreements, it'd be worth listening to.... but simply getting angry about it accomplishes exactly nothing.  For now, leave them in custody until someone figures out what to do... and calm down.