When Rules Fail

When disaster strikes, why does law and order break down almost immediately ?
Whether it is a natural or man-made event, why do the people in the vicinity sudenly act as though laws don't exist ? During electricity failures some cities experience looting. In the aftermath of Hurricane Katrina there was intimidation and shootings. Race and poverty-related riots occur frequently in major cities. One minute the citizens obey the laws and then something triggers the citizens to disregard the law.
Could it be that laws are only tolerated and functional in a society when everything is peaceful and properous ? Is a large percentage of the population secretly desiring to steal and maim, but only act upon their depraved impulses when authorities are distracted and they are likely to avoid punishment ?
When the World Trade Center towers collapsed and the streets were full of dust and panic, did the authorities prosecute those who jay- walked or stole drinks from shops ? Were child-care workers who commandeered shopping trolleys to take the children to safety charged with a crime ? Are laws against theft less valid during an upheaval? Is it the law (and the likelihood of enforcement and punishment) that is deficient, or are people the problem ? The teenager who stole a bus in New Orleans and drove dozens of hurricane refugees to safety was initially arrested, but quickly released and forgiven by authorities.
The only possible explanation is that laws do not apply equally to all people and do not apply equally through all circumstances. When legislation is passed and proclaimed, the politicans neglect to tell us WHO is exempt and WHEN they are exempt.
Why doesn't the law itself enshrine exceptions eg "It's illegal to steal a bus, but we'll turn a blind eye if it's for a good cause." ? Or "It's illegal to loot clothing from a shop, but if the streets are knee-deep in water, we won't investigate too thoroughly."
Are citizens assumed to be intelligent enough or cunning enough to know when a law doesn't apply on a particular day? If so, then good citizens who obey every law may find themselves at a disadvantage when trouble strikes.
Survival requirements, poverty, and a desire to acquire possessions, in combination with a reduced likelihood of being caught, seem to be the main motivators for a person who is deciding whether or not to break a law.