The Chicago fire and Hiroshima were not natural disasters that happen on a regular basis. San Francisco, on the other hand...well that's got a lot of potential to be. I keep hearing warnings about how the big one is coming, just like here. I'm not opposed to rebuilding; I just don't want to see history repeat itself and this one seems to be more likely than the others.
And about half of California's water supply depends on a levee system far more fragile than that of New Orleans - in the Sacramento Delta. It could be taken out by a moderate earthquake or a real good storm, and we had one of those 50 years ago which almost brought down the Golden Gate Bridge - my father drove the next to last car across it to the north before the Bridge was closed from swaying too dangerously.