the thing is- Aang himself understands that his strict adherence to his values is not always a positive thing, i remember in one of the comics (or a later season) he outright calls it his own flaw

if not for the lion turtle giving him an alternative moments before, he’d have to either kill, or watch the world be destroyed

he later has to face that flaw again (actually this time) in the big graphic novels that came out, they’re really good btw. give them a read if you have the time to spare