Yes, this is more or less my point: Case A (Sarajevo): there is a massive unrest, basically what amounts to a Civil War, then yeah - having access to firearms

Yes, this is more or less my point: Case A (Sarajevo): there is a massive unrest, basically what amounts to a Civil War, then yeah - having access to firearms and military training is probably a key factor in your survival (you also have to decide what side you are on, though, which in the long run will also become a key factor in your survival, no matter how well trained you are). Case B (Kathrina): there may be individuals or small groups that take a chance at looting deserted buildings. But they will have basically the same problems as everyone else (surviving the storm peak, being able to move around after the worst has passed). Situations where large, well-armed gangs siege you in your home which has remained intact and holds some kind of resource which is valuable outside of the disaster area (i.e. large amounts of cash, valuables) and you have to fend them off for days until the cavalry finally arrives seem to be extremely unlikely outside of a movie script. You seem to imply that all "disasters" will end up like Sarajevo, my idea is that your reasoning applies only in cases of a natural disaster hitting a region where a civil war is already going on.