Justice League Unlimited presented two little seen aspects of Batman as those that made him unique amongst the Justice League. First, that he is a man who feels very keenly the pain of children (for obvious reasons), and that he is a man who can’t stand to see a child be completely alone (for the same obvious reasons). Those two details, set in conflict with his obsessive need to be a costumed vigilante, make the subtlest, saddest, and yet one of the most compelling arguments for “why Robin,” in any medium.
(For context, the little girl is Ace, she’s been engineered and raised to be a psychic torture machine. She’s dying because brain overload from evil science. The Justice League understands that they don’t kill her, she’ll leave half a city comatose when she dies. Batman volunteers to go in alone. Instead he sits with her, and she dies calmly, killing no one.)