In one sense there is no single universal value, like Marx believed there was: Value, like beauty, is in the eye of the beholder. And yet the difference between a life-affirming principle and a life-destroying principle is the difference between thriving and extinction. So my goal of a society that sustains the lives of humans as humans (as opposed to savages or slaves) is hardly something that needs to be justified. It's axiomatic, IMO. How could you begin to convince people that the goal they should be orienting their life around should be death & destruction?
This destroys everything you say afterwards. Plenty of people are suicidal; you have no reason that they shouldn't commit suicide if they want to. If all of society wants to commit suicide (or destroy itself), likewise. The problem is that you're reading a certain universal value into life that you've just admitted you can't justify - it might be of value to one beholder, but that of course doesn't make it objectively so. Just like you can't explain to a person that their life has an ultimate value (whatever relative value individuals place on a person's life is not 'guaranteed' - it could dry up at any time; also, a person doesn't have an objective reason to value anyone else's relative value of him or her), you have no justification for a law that's banning others from or punishing murder. After all, what justification would you have to make others recognize the value you have placed on a certain thing? It all really does become 'survival of the fittest' in this worldview, and the worst part, from my point of view, is that everything that happens would be justified by it's own lack of needing justification.
So my goal of a society that sustains the lives of humans as humans (as opposed to savages or slaves)
"Savage" and "slave" become purely relative terms from this worldview. As does "human," actually (which is why a fetus is considered less human to some these days). Your worldview does not provide you a justification for seeing to it that anyone else holds your values and/or visions of those ideas. Your goal, then, falls flat.