Good is doing what is right according to the societal culture and norms and the rules stipulated by the very society one lives in and this is what leads to a good life.
Killing is not an honourable act and will leave batman with feelings of guilt and also receive resentment from the religious society as well. The best thing for batman is to take Joker away from this community and city people to a faraway place and have him locked there. This will prevent joker from finding his way back easily in case he ever escapes again. Batman’s conscience will be clean and he will not experience the guilt feeling from killing since this is the right thing to do. Others who have been hurt may not agree initially with batman’s decision but by not killing, batman also teaches the young children of the importance virtue of what is morally right in the society and how they should always resolve their conflicts which is through not always reverting back to violence as it makes things