No. You should help. They're bastards, they attacked an innocent town and killed at least one person who had never hurt them. The moral thing to do here is make sure they stop and can't hurt anyone else.

But I think you're trying to differentiate something you can't. If you're helping one organized group fight another organized group, it's a war. And whether it's making potions, drawing maps, or firing a rifle, it all goes towards the same end: destroy the enemy's ability to fight this war and, hopefully, the next.