How about this one? If Satan is the "Father of the lie" ( ) and all the bad that is in the world stems from both him and his demons (once angels, took his side even though they were perfect ) and all those doing bad things are doing so because of them. Why not just kill off Satan? Why destroy more than 99% of the world's population when you can just destroy the source of all the evil in the first place?
Not to mention... imperfect behaviour is accepted (to a certain extent) because we are imperfect. But if Adam and Eve were perfect, why then did Eve listen to that snake?