In the bigger picture, there's one common set of ethics that can be agreed upon. Remember, ethics and morals—while oftentimes shaped by culturally unique standards, expectations, and needs—are forged through fundamental aspects reached through logic and reason. This is at the heart of most philosophy, the idea that morals and ethics can be given proofs through rational deduction.

All that to say: Morality is, ultimately, something that can be derived without a specific culture telling you what is and isn't moral. Morality can be derived logically, and the fact that vastly disparate cultures can come to the same agreements does a lot to prove that.

And I think that you're "you're not seeing the forest for the trees" argument is a bit disingenuous. I can see that it's a forest. I also can see that thee forest is made up of individual trees. You're suggesting we never evaluate a forest by its trees, and I disagree. A murder murder of a non-combatant is a murder of a non-combatant. It's important not to sugar-coat that fact or attempt to forget it.

Actions should be evaluated within their contexts (or forests, to continue the metaphor), but their contexts don't make it any less what it actually is.

Throughout human history there have been times where it seems blood must be spilt because blood has always been spilt and that eye--for-an-eye warfare where both sides devolve into monsters is simply "how the game is played".

But thankfully there were people who said no, people who spoke reason and were able to hold themselves to reason and moral standards.

You can debate whether murdering innocent children is alright. I'm a bit saddened that you'd actively argue for the murder of innocent children under circumstances that favored it, but I'm glad that you'll never be put in a situation where you can murder children.