Can't be a King without subjects. Can't feel like a God without control. What makes Imu truly evil is that he has the power to make the world a utopia but chooses to make it his playground. You can only force people to kill each other for so long until it get's boring. And that's where his true malice lies, in the fact that he doesn't want to end the story, he want's to write it. Imu is not a destroyer, He's a megalomaniac with a God complex who want's to be the author of the world and tell a great tale where he is King, where he wins, while everyone else is just playing their part.