They are literally doing their jobs: enforcing the Constitution, including the checks and balances built into the three co-equal branches of government. If the government proves its case, the people get deported. While they are working on it, they remain confined. That's how it works, and how it has always worked. Presumably the government will have no trouble meeting the low burden required to deport people if they have caught dangerous criminals.
If you start to pick and choose which parts of the Constitution get enforced, you lose the Constitution. Surely that's not what you want.