Humans are gamblers. It all comes down to the cost-benefit analysis. I live a few miles from Malibu, where perfectly rational people buy multi-million-dollar houses perched on shaky bluffs. I've been in California for 22 years, and have been smack-dab in the middle of two massive earthquakes (in San Francisco in '89 and in LA in '94), not to mention riots and wildfires. Yet the benefits outweigh the costs.
There's lots of talk of costs and benefits now, after levees built to withstand catagory 3 hurricanes have been breached by a catagory 5/4 Hurricane Katrina, and the newspapers are observing that back in 1778 engineers warned about building a city in the topological bowl surrounded by water that became New Orleans. Yet New Orleans has survived over 200 years of hurricanes (including at least one that caused the nearby lake to break levees and flood) and prospered -- until now. It's just a fact of commerce that cities with waterways become successful ports -- and yet water always presents a danger. A cost-benefit analysis.
Yes, the finger-pointing has begun, and will likely continue long after the flood waters dry up and the lost accounted for. Humans aren't just gamblers; they want someone to blame if they roll snake-eyes. But in the end it's all a cost-benefit analysis. This time, the cost is shattering.