First of all, I don't buy in to the equally powerful, ying/yang black/white evil/good dichotomy. I figure that good is inherently greater and more powerful than evil. Light is action and energy, and always defeats darkness. Darkness is inert, nothing, an absence of light.
I am not sure that evil exists as an independent force, but I do believe that men are capable of evil acts. This ability is necessary if we were truly created with free will.
When I suffered under an evil man, I wondered what took so long for God to answer. I don't believe a loving God would be impersonal about watching me suffer. Was He unable to intervene because of His self-imposed decision not to interfere with man's free will? Does He view our suffering differently, maybe likening it to a doctor's needle? Perhaps from his point of view, the pain is short-lived in light of eternity.
Even now, my pain is only a memory, it is not a handicap. Rather, my experience has made me empathetic of the others' pain.
Perhaps a few horrific events and tyrants affect society's soul, and wisen us up to avoid future horrors. No one wants another Hitler to succeed. The fear of another Hiroshima has kept our nuclear weapons mouldering in their caverns, thank God.
I believe there is ultimate justice, at eternity. I wish eternal torment on Hitler, and I pray there is eternal comfort for the young, weak, and old who were overcome by evil here on earth.
Even if my theism is myth, wouldn't this belief mark the way I treat others, now? If I truly believe good ultimately wins, wouldn't I do my best to live that good life, now?