The story put a long-debated paradox of human justice in the context of a hypothetical scenario, but I don't think it concluded the case. Personally I don't think the end justifies the means. The story demonstrated how power corrupts, but it's a paradox because not using a power to stop corruption could be also counted as evil. But according to some, abstaining from intervention is wisdom and what it takes to be a sage. I think Light wanted to be something he isn't- a god. Hence he was delivered divine punishment from Ryuk. There is or are (a) philosopher(s) who say(s) that all moral claims are authority claims. 'Who says so'. Light had the power - but there was another authority above him (Ryuk). Hence humans should never play God, unless they are prepared that there is indeed a God who will judge us. I think the story could have been more interesting had there also been a 'Life Note' that can resurrect those whose name is written in it.