Locking someone up forever without proving guilt destroys the rule of law. If the state has a case, it must bring charges and face a court.
Indefinite detention also corrodes the institutions doing the detaining—prosecutors get lazy, evidence rots, and accountability vanishes when there's no trial deadline forcing the work.
Even with judicial oversight, indefinite detention undercuts due process and invites tyranny; the rule of law demands charges, evidence, and timely trials.
Even with oversight, indefinite detention undermines the innocent until proven guilty principle. Power without timely, fair trials is tyranny; the state must prove guilt in court or release.
Even with oversight, indefinite detention makes liberty depend on officials; the rule of law demands timely trials to protect the innocent, not endless delay.