A missing scene that fixes everything!
So here's my theory about why the characters in this film behave the way they do.
In Hitchhikers Guide to the Galaxy there was a planet called Golgafrincham. They gathered all their management consultants, hairdressers, and telephone sanitisers onto an ark, and sent them off into space.
Before the mission portrayed in Prometheus, something similar occurs. The scientific community decides to rid itself of the most hopeless and pathetic scientists in their fields, so they gather them together, tell them they're going on a special mission - the first of its kind! - and that they're counting one them to do lots of good science while they're out in space.
Then the people remaining on Earth launch the ship of no-hopers into deep space, and breathe a collective sigh of relief. Making the world a better place for the cost of one spaceship.