@Mor - The problem is that often people take it a step too far. The causes of the Great Depression are varied and unfortunate, not just down to a banking mistake, and even during that terrible time there wasn't widespread looting and murder. People who identify as preppers often seem to think that the rest of the world is only one step away from losing the veneer of civilization and that they are going to end up in a bunker with a shotgun desperately trying to defend their cans of string beans.
In reality, if anything happened I think it would be more likely to be a gradual thing and that most people would join together and help each other out. Which is what happened in a lot of places after Black Tuesday.