There was nothing "acceptable" or "normal" about the loss of the Challenger or Columbia and the Crews, in fact both Disasters were very much Preventable. Truth of the matter is corners were cut for political/budget reasons and 14 astronauts paid the ultimate price, along with the loss of two Orbiters, each with a price tag close to two billion dollars.
You always downplay incidents and like to use the term " normal failures" alot. parts do fail without a doubt, thats why time limits, Inspections, parameters, overhauls are so crucial and meant to avert the potential failure. prevention and safety go hand in hand, when corners are cut and cost come into play, you have just eliminated that safety net.
Airline disasters are rare but when they do happen the results are usually catastrophic, what worries me is this general overall false sense that outsourcing is just as good but cheaper. the Government, and the airlines both point to the fact that with the recent years being the least accident prone as proof., well we better all hope they're right for once. As they say "Even a blind squirrel finds an Acorn every now and then"