God, the fact that so many people here agree with the hero is unsettling.
It should be blatantly obvious that the point of this is not 'Save the world', but rather to improve upon the world as a whole, and to improve the personality, skills, and morals of the hero.
If the heroes are sent back to earth with their powers as it seems is the case, the end goal is likely to create a bunch of righteous and good heroes to make earth better. Maybe for a fight against some other force, who knows.
But the way the hero goes about things is simply psychotic. He murders because people are annoying, he doesn't care about innocent casualties as long as he gets what he wants in the end.
The reason his reputation was low isn't because 'People pinned the blame on me!!' it's because he was a ruthless dictator who murdered people on a whim, and only cared about getting stronger just so he could leave.
It shows that he doesn't have empathy, or a passion to help others. He's a psychopath who will kill those that annoy him or thst he can gain from.