Always disliked the " We must not become like them hurr durr" .
Sometimes responding in kind is warranted, like in immediate self-defense situations.
However, most of the time, "not becoming like your enemy" is the best thing to strive for, or else you just create more victims and future enemies.
If they'd gone with the kid's plan, then it just would have left a different territory to starve, with all the civilians suffering unjustly. Just like how theft in general eventually harms everyone in the local area, if it gets widespread enough, like what's happened in several US cities the last few years.