It is one thing to recognize that evil exists. It is quite another to decide that, no matter what one does, one will never be able to reduce the amount of evil in the world, and it is exactly this which Candide decides for himself at the end of the story.
Evil is a uniquely human attribute and derives from human nature.
I simply do not agree that evil is inherent in human nature. This may seem odd coming from someone who not long ago was accused of being an absolute pessimist. I realize that orthodox Christian dogma requires us to believe that man's nature is corrupt, but since I am not an orthodox Christian I do not fell compelled to accept such a proposition on faith. I have often heard the argument that evil must exist in order for mankind to know the difference between good and evil. I have never thought this argument to be valid.