I agree with Sam. In the end, the captain has the responsibility. Even so, Captain Smith is really only responsible for his part of it.
This is something I've thought about a lot, because it came up in my book about Thomas Andrews (which, alas, has STILL not found a publisher, but it's ever vigilant in looking).
I have a scene, during the building of the Titanic, at a time when several men died in shipyard accidents. Without going back to my notes, I think it was in 1910, over a space of 3 or 4 months, at least 4 people died. In my book, Tom Andrews has met time travelers from our century and he knows what happens to his ship. He's trying to prevent it. But with all these deaths, he confronts one of the time travelers (if you'll permit me to quote from my own book): "Three this month, four in just two months. That has to mentioned somewhere. Did you know these people were going to die, Sam? This is not all just about me. It's not all about the sinking. People die, Sam, building these ships. If you know these things, you have to tell me. We have to stop everything we can."
From there, the time travelers acknowledge that even in the future, business seldom does everything it should to make things safe. No door handle on Apollo 11. The 0-rings on Challenger. The shielding on Columbia.
We know these things need attention, but it's easier to let it slide. Maybe it costs too much to fix it. Maybe it will set the schedule back for a year if we bring it up. But I think it's human nature to put things off until we are forced to deal with it.
It's possible no one thought of it. I've heard that Titanic sank because of a lack of imagination - no one could envision the circumstances that would bring her down. Yet all the signs were there, weren't they?