If we're being super technical, it's not actually illegal to be in the US without proper authorization in most cases. Most entries don't involve bypassing border controls, which is a crime. So in normal circumstances if you overstay your visa you get a notice that you need to leave.
The claim is that because they're just being removed and not charged with a crime, putting them someplace like that is just holding them for deportation and not actually punishment. Since they're not being imprisoned they don't get due process.
This is hogwash, both morally and by the actual law, both the letter and intent. Even circumstances that actually do kinda work like that don't work like that.
As an example, a drivers license is legally not a right, but a privilege. Failure to comply with certain stipulations results in an immediate suspension. But oh wait, even then you still can have a hearing to dispute things in the most incredibly cut and dry legal circumstance.
You're supposed to get a proper hearing before anything happens so that you can dispute a removal order and such.
True. Italian as well. Proportionally not nearly as big though, so they don't come to mind as readily.