I'm not sure of the reason for your question, unless you are not an American or if it was simply a bait question. If people arrived illegally, our Constitution guarantees them due process. The major causes of public outrage are the methods used to capture human "prey" and the denial of due process.
just seeking clarity — I don’t entirely understand what’s legal and what’s not — and the ACLU statement doesn’t give context. Under what pretext are these people detained? What should have happened that didn’t?
The rationale that the despot has long used is that illegal immigrants are a threat to national security because "they're all criminals" and he's "protecting," us from them. Under that guise, he is casting his net to chase, capture, detain, torture (conditions at camps) and disappear people.