The thing about Superman is he just has no boundaries. He can actually walk up to Assad or Kim Jong Un in their bedrooms and tell them personally to stop their shit, without any diplomatic or bureaucratic crap. If there is a raid on a village in Africa, he can swoop in and stop those crazy motherfuckers. If there is a hunger crisis, he can just take/borrow/steal food from anywhere and let it rain on those who need it. When the world leaders can't decide to reduce the amount of nuclear weapons, he can grab the bombs on all sides and throw them away. Nobody could stop him from doing so. He could do all the right things that are prevented by the boundaries that are self imposed by our society, politics and economy. And since he doesn't represent any nations, his actions would not cause wars between countries or factions.
My favorite scene from Iron Man 1, where Stark just goes into the village attacked by the terrorists, when the US military doesn't act. Because superheroes can act when all others decide not to.