When Browns Ferry caught fire, lost all control systems, and came withing 30 minutes of a complete meltdown in 1975, it was the "safest reactor design" in America.  And really, the design engineers themselves were surprised--but they hadn't counted on a fire burning the insulation off BOTH sets of (the redundant) control systems.  

Three Mile Island is more famous.  A third of the core actually was destroyed, although the last minute restoration of cooling prevented the rest from melting through.  

It is hard to maintain elaborate safety proceedures over prolonged periods of time (decades) especially if they cost money.  

What you call the binary nature of failure is an important point that may deserve more emphasis.  Annecdote:  I am reading a book on arcitechtural materials and get to the part where it describes that glass is never used as a structural material.  While I am thinking, yeah? so? I read on:  Glass is both stronger and cheaper than steel, can be conveniently shaped, on and on, really, it is better than anything, just ideal!--except:  When a glass structure fails, it almost always fails without warning.  One moment it is (looks) fine, the next it is collapsing completely and catastrophically.  So:  Despite its many attractions, architects just don't use glass for load bearing-parts.  

Which is a long way of saying:  Some technologies simply cannot be used.  Despite any, perhaps many, benefits there is no wisdom to it.  

The Fates are kind.