The fundamental problem, and actually the crux of THOUSANDS of debates, is the fairly silly but almost universally-held belief that human life is priceless.
Of course, you mention that you believe that human life ISN'T priceless, and you're immediately subjected to a torrent of flames.
But even a cursory examination of how society spends its money, makes decisions, reveals there's a price on human life...I've seen various studies that actually attempt to calculate it....but problems come in when people try to pretend there ISN'T a price.
How does this relate to the Space Shuttle program? If we really believed human life was priceless, we'd put 7 people in the thing and never launch it and play movies of space outside the windows.
Obviously, that's one (unrealistic) extreme. But to accomodate the various fixes recommended in this thread (All flights being able to reach the ISS, having a shuttle always ready to make a rescue flight, etc.) SERIOUSLY degrade the ability of the Shuttle to do useful things, and also likely cost vastly more money. There's a balance point you try to reach but there's no obvious guidlines to find where it is.