[Kanji_The_Wanderer]

Sure they can kill mass quantities of people. The Death Note cannot end, it will just keep on growing every time you get to the end of it. So if a group of Shinigami sat around all day and just wrote down names, then in a short time, the human populous would decrease drastically.

Kira has the powers, but you are forgetting that everything is made up of rules. Since the beginning of time, it has been deemed evil for humans to kill each other. "It goes against God" that is what humans believe. It is a sin to kill each other. Kira is killing people, so he is a murderer. If you kill someone, for any reason, it is still against the law. Yes killing out of self defense can be excused, but it cannot be denied that a human is dead, so someone will hate you for it. Kira kills to create a world that he wants, only to allow people in it that he sees fit. The world should be run by people as a whole, not just leave it up to one person.