This is actually a thing that theists say to atheists a lot: "Without God, you atheists have no foundation for morality. There's nothing stopping you from raping and murdering."
I find this statement horrifying, since what the theist is actually saying, almost certainly without realizing it (EDIT: and likely without intending it, as it probably doesn't really align with their values), is that they want to rape and murder and only their belief in God is holding them back. God forbid that they should someday lose their faith.
Um, no, that's not what we're saying. As a theist that makes this argument, I am quite clear that this is not what I'm saying. Let me try to explain what I am saying in a clear fashion.
Morality--the idea that some things are wrong for everyone and other things are right for everyone--is either a true idea or it is not. Either killing an innocent and non-threatening person (for example) is wrong for everyone, or it is not.
Morality cannot be mathematically proved. There is no possible series of equations that can prove that it is wrong to commit murder--that is, to kill an innocent and non-threatening person.
Morality cannot be empirically observed. Unlike gravitation and magnetism (for example), there is no empirical experiment which can demonstrate that it is always and everywhere wrong to kill an innocent and non-threatening person.
Perhaps murder is wrong because I dislike it? If it is wrong because I dislike it, then at most I can say that it is wrong
for me. Under this model, for someone that does not dislike murder, such as the infamous serial killer John Wayne Gacy, murder is not wrong. This is basically similar to different flavors of ice cream. The most I can say is that a given flavor is wrong for me; I cannot say that it is wrong for you.
Perhaps murder is wrong because it is counter-productive? But then, under any circumstances where murder is not counter-productive, murder is not wrong. For example, Hitler and his Nazis dreamed of a Jew-free Europe, and ultimately, of a Jew-free world. For them, the mass murder of Jews would not be wrong under this model, because it would not be counter-productive to their goals.
Indeed, your story has provided examples of the protagonists, our beloved Hazo and Team Uplift, committing mass-murder and justifying it by appeal to the utility of it. I'm thinking particularly of the sinking of the boat scene, as well as Hazo's consideration of joining in the blood-crimes of Orochimaru because he supposes that ultimately the torture and murder of a few dozen innocent people will lead to some kind of utopia. The Communist revolutionaries in Russia, China, and other countries trod a similar philosophical path.
Perhaps murder is wrong because it is illegal? But murder is not always and everywhere illegal. Under this model, the wrongness of murder depends upon the local criminal statute.
So what is the basis for the assertion that murder (or any other act) is wrong everywhere, everywhen, and for everyone? The only basis that I can see is the decree of G-d. If you do not believe in Him and His law, then the most you can say is that you find murder very off-putting, or that it is usually counter-productive, or that it is illegal, but not that there is anything inherently wrong in it.
In contrast, I, as a believer in G-d, can say that not only do I find murder very off-putting, but also that it is wrong, always, everywhere, and for everyone.