In the Yin/Yang philosophy it states that opposites are necessary in order to create the universe. If
this is the case, since one polar is considered to be "good", the opposite polar being "bad" or in the
case presented "evil", is evil a necessity in order to create balance in the universe?
The Yin/Yang philosophy, as you call it, is about balance,not opposites. It is the Taoist philosophy in
fact. Good and evil are not postulates let alone abstractions, they are what is the case if we examine
our bodies or the world around us (i.e.. our experience and that of our families). There is a circular
relationship between the two, rather than an oppositional relationship, in this philosophy. Good health
becomes bad health if it is too good, e.g.. the growth of cells becomes cancer after a certain point.
Beauty becomes ugly and so on. Cold burns us, heat eats us away like cold. The truth lies between,
in the balance. The Yin/Yang philosophy, as you call it, is an avoidance of extremes. Its main
postulate is a middle way.