You don't have to. There's no compulsion. But if you thought omnicide was justifiable then I can't see that you could claim anything else could be deemed unjustifiable. Literally anything goes. And the very best that could be said about it would be 'Gee, there must be something that makes it morally correct but, I dunno, I just don't know what it is'.
I can see how this might be a concern, and I think it's a legitimate one with all of the crazy things that go on in our world. But in offering your evaluation of me, you now have me concerned about you. You say you can't see how an ancient account of a so-called act of “divine omnicide” doesn't actually translate into an across the board directive for any Christian simply to drop what they're doing and go and attempt to do likewise. Really?
So, tell me, Bradskii, how do you think any of us should be making moral justifications? Do you think there are any multivariate levels of social, psychological and/or ethical complexities present that we need to work through in order to discern distinctive nuances that may be at play in our moral deliberations? Or, do you instead think that “morality” is a simple thing to figure out?
At this point, I want to also bring your attention to the fact that a little earlier in this thread, I and a few other posters were originally discussing the essence of the term “genocide,” a term which I think is more readily comprehensible and more common to our historical understanding of our world than is “omnicide.” The semantic difference between these terms being not too dissimilar from that of conceptually comparing things like “The Holocaust” and “Dr. Strangelove.”
I've never really had a problem in discerning between real life and make-believe, or between my own human ethical outlook and a divine one that is clearly encased within the conceptual matrix of an ancient, foreign culture.
And that will be the justification for any atrocity: 'I'm certain it's what God wants'. So I don't have a problem with God's sense of morality. My problem is with those who will accept anything that they think His sense of morality will allow.
Whether fortunately or unfortunately, knowing what “God wants” is a complex thing, even a complicated one. This is peculiarly so where the application of moral tropes from the Bible is concerned, and in this, I think we can both acknowledge that it's those who think Christian moral deliberation is a simple thing who have the most problem in sorting out their emotional penchants for unjustified violence from authentic moral actions.
I also think that some of the social and psychological dynamics at play in the kind of religiously entangled moral discernment you're alluding to is what separates a Saul of Tarsus from a Paul of Damascus ... ... and I'm sure some amount of solid Hermeneutics plays an important part in this as well.