everything is in relation to something else. If there is big, there has to be small, if there is opened, there has to be closed. The same with good. If everyone was good, then no one would be good. And if there was no murder/rape/incest(all promoted by the bible btw) then we wouldn't have gotten rid of evil. We would just make things like running a red light evil, because it's all in relation to it's opposite.