@jokerxhisoka:
In short: You seem awfully certain that the country in question doesn't have mandatory conscription.
At length: Heck, even in the rare, full-time-professional armies like modern-America's where people
did all choose to sign up, for a lot of people it's a calculated move of economic necessity, wherein you hope that the mostly-peacetime army you're in stays that way 'till you get out.
Even if that weren't true, your reasoning (they are soldiers, so it's fine to just kill them all) is childish, the sort of mindless drivel that has no place outside of indoctrination and propaganda. There's really no moral excuse at all for slaughtering an army that you didn't have to. And while there's a lot of leeway there, "They would have killed us if they had the chance, which they didn't," is
not one of the justifications for wholesale slaughter that we generally accept. Thus, for instance, when the enemy surrenders, you're supposed to
stop.
I mean—you could argue that it's a revenge-killing, and then you'll have to deal with some other branches of ethical reasoning, but that's not the argument you were making. Alternatively (and also not the argument you were making) as an unholy sacrifice to resurrect your friends, it's at something we can
empathize with (but still by almost any moral or ethical standard I can think of, nonetheless a big "no-no").
But implying, "a soldier's life is worth nothing, because they choose to kill and die" is, while a pretty good line for a gritty war-drama, just absolute shit ethics.