"We are going to have failures. There are going to be sacrifices made in the program; we've been lucky so far. If we die, we want people to accept it. We are in a risky business, and we hope that if anything happens to us it will not delay the program. The conquest of space is worth the risk of life." — Virgil 'Gus' Grissom.

It seems like most of the Mercury/Gemini/Apollo era astronauts felt like their lives came second to mission success. I'm sure there are plenty of astronauts that feel the same way today.

With a pool of astronauts willing to take reasonable risks to advance space exploration, it's the NASA management that has been responsible for disallowing the more dangerous missions. On the one hand that's tragic, but on the other it makes sense from a PR perspective. With each spaceflight tragedy there has been a backlash from taxpayers and Congress. Politicians will use spaceflight accidents to push agendas that cut funding, etc.

NASA has to walk a fine line between keeping the program safe enough to maintain funding and adventurous enough to make gains in space exploration. I think in early NASA it was easier to justify the human cost of accidents because of Cold War pressure, but now there is a harder time with this justification and thus the huge emphasis on safety.