Defending anything meant fighting the Siren army. Who else were you fighting with?
War's more complicated than who has a gun and who hasn't. It ain't like criminals battling it out in Hell's Kitchen. Civilians can be complicit in oppressive regimes. What if this land had been stolen from the Sirens? What if they were being exploited for labor back in their own territory, wherever that was? I'm not saying that's true, just that it could've been, and not knowing bothers the hell out of me. Whatever we did, big or little, it contributed to their loss. We might've changed things for the worse.
You're gonna do what you're gonna do, I don't expect to change your mind. Just explaining my reasoning.