Answer:
   
   First off, Jews certainly do maintain that there is good and evil in
   the world. But let's clear up some terms first.
   
   Consider the parameters of good vs. evil. Imagine a line going from
   -100 to +100, with -100 being evil, -50 being "bad", 0 being neutral,
   +50 being "good", and +100 being pious, like this:
   
-100 (evil)----- -50 (bad)---- 0 (neutral)----- +50 (good)---- +99 (pious)

   The Jewish tradition acknowledges the entire line, and cites examples
   for each point. It also contends that most of us only go from, say,
   -65 to +65. However, it also acknowledges that we're capable of going
   from -100 to +99 (for only G-d stands at +100). And it offers that G-d
   has provided us with the mitzvah system both as a barometer of what's
   -100, -65, -50, 0, +50, +65, and +99, as well as a means of attaining
   the full human potential of +99.