I don't think they regard the Hubble flight itself all that terrible, just that in case of another Columbia event where the Shuttle couldn't re-enter safely, there wouldn't be a backup Shuttle to rescue the Hubble crew.

On a Moon or Mars mission my suspicion is that everyone would accept there would be no backup.

Which do indeed leave the possibility of the folks stranded until the consumables ran out. Imagine what would have happened if the LEM escape rocket hadn't fired. I know it was hypergolic, but a pipe could have been plugged, or bent, or something.

Wonder how much redundancy they'd have to have on essential systems.

Arf