The problem, of course, is that the global rule trumps any situational common sense, any discretion. But in granting discretion those in overall charge must trust people below them who have more detailed situational knowledge. It's CYA security -- the same thing you see at airports. Those involved in the situation can't be blamed for making a bad decision as long as they follow the rules, no matter how stupid they are and how little they apply to the situation.

Here, here ...