>without the bad you can't appreciate the good

[Aoi Magi]

One can argue that bad doesn't really exist and is just an absence of good, because at the end of it all, what we call "good" is defined by our own morality. But I personally fill bad is necessary to know good, because our morality is shaped by these bad things which ultimately allows us to define the good, and the "bad" isn't something limited within our society but is applicable to almost everything in nature to some degree.