1. Why do you think this was an engineering failure and not a business/implementation failure? For instance, in that famous pedestrian bridge collapse (a pedestrian walkway in a hotel in I think Kansas City collapsed shortly after opening, killing and injuring an absurd number of people), the bridge was designed correctly, but a deviation from the design in construction led to a fatal flaw.

2. What do you consider "perfect"? A lot of things aren't engineered to be perfect, because that's expensive. Instead, a lot of questions -- like with sea walls -- resolve around things like "ten year storms", "hundred year winds", "thousand year earthquakes". It's very possible that the flaw in this design was considered, but it was concluded that it would take a once-every-thousand-years disaster to breach the sea wall and cause a problem. Everyone involved may have agreed that a 1% chance of failure of the lifetime of the plant was acceptable.

Everything is a cost-benefit analysis. At some point, risks are declared "small enough" and everyone agrees to move forward. In this case, a regulatory agency in Japan -- representing the interests of the government and people -- could very easily have signed off on the risk posed by the positioning of the generators.

And more importantly, just because a small risk ends up being realized doesn't mean we were wrong to take it in the first place. Negligence can cause accidents, and negligence can exacerbate accidents, but also sometimes shit happens. Wasting time, money, and people trying to shrink a one-in-a-million risk just because it happened once is stupid, and we do it all the time.

Third, an obligatory "do you even know how bad coal is?" A hundred thousand miners in the US died mining coal in the last century. 6000 died in China in 2004. "Oh no," you say, "nuclear is extra bad because it poisons places for hundreds or thousands of years!" Underground coal fires: a seam of coal exposed through mining can catch fire and burn underground forever. We have no way to put them out. The most famous of these is in Pennsylvania, where a town had to be abandoned because the coal mine underneath it was burning and releasing noxious gasses up to the surface, along with the occasional flaming sinkhole. The fire is expected to keep burning for hundreds of years. There are dozens or hundreds of fires like in the US, and dozens or hundreds more in China.

I wouldn't want to go swimming in that water released from Fukushima, and by all accounts radiation poisoning is a terrible way to day. But so is being crushed to death in a mine collapse, or slowly starving to death underground in the dark, or dying of the various cancers and ailments related to the carcinogens coal plants routinely belch out. Everything we do has risks, from driving to taking a shower to building power plants.

You are presenting a false dichotomy: the choice is not between a world with nuclear disasters and a world with no disasters. It is a choice between nuclear disasters and non-nuclear disasters. We should seek to minimize the chance of nuclear disasters, yes, but we shouldn't treat them as "special" just because they're "scary". We should weigh the risk of a nuclear plant against the risk of non-nuclear plants, fairly, and make the decision that saves the most lives.