The fact that someone can be temporarily jailed without any evidence or a change to challenge the charges is a painful compromise that the Founding Fathers made to balance justice (they themselves were at risk of arbitrary imprisonment by the Crown) with order (sometimes you see someone running with a bloody knife and you should arrest him before you trace his steps to find a corpse). Police departments try really hard to push what they can get away with, and there are certainly areas where I wish the courts would constrain them.