You are not a nut and have the right to take the angle of vision that you chose. As for me, I think the value of life is defined how well it suits survival of the species, then a nation, then a family, then an individual.
In a situation with a girl and a hag, you are choosing the girl not because she will have more chances to enjoy her life than an old hag, but because she can have children, thus perpetuating the human species.
In the situation in the mountain, the boundary conditions that matter.
Again, what would allow more people to survive?
The positive impact is the same thing. The more positive the impact that an individual can make the more it is conducive to the survival of the species.
It's a different thing that each individual usually values his own life more than everybody else's. That has little to do with the general value of life and more with the fear of death.