I thought about it and realized had Aang out right killed Yakone the man wouldn't have escaped prison, used his connections to get face change, fone to the North Polem and have children who he instilled his hatred into. I am not trying to attack or bash Aang, because he was human and of course he wouldn't have known Yakone would break out of prison or have children that would inherit his abilities. The tradition of a previous Avatar's actions come back to huant later Avatar. Roku didn't kill Sozin, becasue he assumed he would always be there to stop him, Koyoshi trained the Dai Lee etc.
At the time none of them knew those decisions would have negative consequences, but they regretted them in their afterlife. I wonder if Aang regrets not dealing with Yakone differently or because of the trouble Tarrlock and Amon caused Korra andRepublic City. Anythoughts?