> Usually they do not hold them for very long.

I am confused here. If the law grants ICE (or whatever is the umbrella agency that ICE operates under) the power to detain to determine legality of the status, ICE does it, and then releases people back, the law works as intended, no?

I am confused what is the difference between this, and police who can detain a “tall man in black short and red hat” and 10 hours later (or whenever) release back due to new information, or mistake in ID?

I understand that we absolutely have to strive to zero of such cases, but operations at scale (like law enforcement) have zero chance to have no mistakes.