Any rule of law must have a process in it for (a) honoring exceptions in the light of higher principles and (b) recognizing the relative importances that make some laws "higher-level" than others -- for example, the Bill of Rights. Arguments about "necessity" because of short term concerns can be used to violate these two intersecting requirememnts, to the detriment of the civilization as a whole, usually. One of the things which provides for (a) in our basic system is the peer-process of judgement, the jury system. However, because our legal system has grown so adversarial, the principles of evidence have yielded to the principle of adversarial weight and force, where truth, justice and principle all take second place to the debating talent of professional liars.