I remember hearing some senior NASA flight controller who was happy to see the end of the moon landings because he believed we'd almost certainly lose a crew if we flew more missions. Beyond Apollo 13, several of the moon missions had serious problems that threatened the mission. I'd wager the odds of success for moon missions was a lot less than 50:1, but there was no shortage of astronauts willing to make the flights. Astronauts, especially back then when most of them came from the test pilot ranks, aren't a risk adverse bunch.

As for something even more challenging like a Mars mission, the odds would likely be considerably worse than 50:1 (10:1 is more like it, IMO), but you'll find no shortage of volunteers.

I do agree that 56.5:1 is poor odds for Shuttle missions given the return, but that's the current state of the art. Space travel was, is, and likely will be quite dangerous for the foreseeable future. I do believe we can do better, just not much better with the Shuttle.