The rest of your point, I think, is a very interesting way to look at the value of human life, but it is a crude way of evaluating the worth of humanity purely in the context of financial value.
At the risk of getting touch-feely amongst an audience that is very rational and analytical, there is something sacred and indescribable of all life (not just human) simply because it's not something that we can create from artificial means. This fact, I think, is what makes it hard to say one life is more valuable than another (again, just to be clear, I'm using 'value' as in financial value).