Well. it has to be based on some value system and science doesn't provide one.
I for one think that human life has some value and so does freedom to choose many aspects of your life. but I can't "scientifically" argue why those values are correct.
To be able to make any value judgement at all, one has to have some "non-science input", some subjective choice.
What I'm saying is that basing those values on some fiction is no more or less "correct" than any other choice, because they are fundamentally subjective choices.