re: The Concorde example
Look at history:
Did the Apollo program stop after the Apollo 1 fire or the Apollo 13 accident?
Did the Shuttle program stop after Challenger ot Columbia?
Did Concorde stop right after its only fatal accident?
No company, no country wants to stop after a failure.
It's a matter of pride.
The shuttle is intimately associated with the US.
They'll stop at a success.
And even if STS 121 is a success, with small chunks of foam falling, it still is needed for the ISS.