It is difficult to rationalize the co-existence of evil and good in human existence. Maybe it is a necessary relationship. Maybe it is the Hegelian dialectic in action. Maybe it is the manifestation of the dichotomy of the way the universe functions...a universe of opposites regardless of the pain and suffering. Wars and their evil regimes do in a way curb over population, hone the technology of science, stir and shift politics and redefine geography. A life with conflict, however large or small, may be an inherent characteristic of mankind. And neither all evil is bad nor goodness good.
I am reminded of a particular scene of Graham Greene's novel The Third Man brought to the silver screen in 1949 staring Joseph Cotten as Holly Martins [a writer of westerns who winds up in post war Vienna at the invitation of his old friend Harry Lime] and Orson Welles [the evil representation of greed and easy money]. Harry has been specifically stealing penicillin [among other things], diluting the drug, and selling the product. It is assumed that Lime had died but Martins doubts the claim and attempts to discover Lime's whereabouts. Finally they meet at an amusement park and board a Ferris wheel where Martin challenges Lime and his activities. Harry Lime finally responds...
Don't be so gloomy. After all it's not that awful. Like the fella says, in Italy for 30 years under the Borgias they had warfare, terror, murder, and bloodshed, but they produced Michelangelo, Leonardo da Vinci, and the Renaissance. In Switzerland they had brotherly love - they had 500 years of democracy and peace, and what did that produce? The cuckoo clock.
Think about it, good and evil just may be an integral part of humanity.