I don't think there's anything wrong with what happned with Aang. The other Avatars were willing to kill,but that doesn't mean Aang has to kill. The Avatars aren't all the same, otherwise it would just be one immortal guy all the time. The fact that they had different viewpoints on what to do about things was pretty cool to me.
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The batman villians all seem to be one big joke that batman refuses to laugh at - SantaRPG