That may be true, but it illustrates an important point: we shouldn't need tragedies to be unthinkable in order to make reasonable decisions about their probability.

We don't do this in every situation. Most American parents transport their kids by car without giving the risk much thought, though car crashes kill significantly more children than homicide in the US (source: CDC). I'm not sure there's a good solution to the cognitive bias of discounting relatively mundane risks.