One of the biggest problems in spirituality is the concept of how and why a God of love would allow evil to exist. Most theologies have a section of writing devoted to this issue - that is, the discussion of theodicy. For some, the problem of evil becomes a barrier to moving forward in their belief in a "higher power". They want "their God" to be all powerful and infallible, and in many ways they want this god to run their lives.
The God of the Abrahamic faiths, however, allows for humans to have and to exercise free will. By allowing this (i.e., not limiting choice) the God of Abraham allows for humans to be evil as well as good. The interaction of Satan with Eve in the Garden of Eden is the earliest example of this.
Evil is always seductive, and usually the most destructive and pervasive forms are cloaked in well meaning answers to human problems. In fact, human solutions to social issues often go awry because we are limited in our ability to see all possible solutions, and forget to "love others as ourselves".
Case-in-point, how is it that the Department of Corrections has become the largest provider of service to the mentally ill? This happened from well-meaning legislation in the mid-1980's which dismanteled the state hospital system. Now, there certainly needed to be reform in that system, but "throwing the baby our with the bathwater" has resulted 25 years later, in many of these ill and poorly cared for persons ending up incarcerated. I don't think that anyone can argue vociferously that this was the intended outcome from that well-meaning legislation - simply that it was an unintended societal evil (i.e., social injustice).
Our only way to combat evil is through opening ourselves to love. The only way we can do that is through study and prayer. Evil will never be overcome, but its scope can be limited by our world view.