They don't have to be 100% safe (though I think they could be
), but if there is only 1 incident ever 100.000.000 years or so, it is well worth the risk. Think about it; you are driving most certainly a car. This isn't 100% either and you are much much much more likely to die because of a car accident than a nuclear accident, yet you still do it. If you die in a car accident this for sure isn't a city wide desaster (well... except for the million c2c players that would cry for you), but for YOU, it is the worst possible outcome - you die.