Evil is not something that god allows or encourages, it comes about as a result of man's free will. We are all responsible for our actions, and we have the free will to choose whether to make the world a better place or to satisfy our own selfish desires and perversions. Adolf Hitler was not born evil, instead he choose to commit horrific acts of violence and cruelty against those who did not share his race or his beliefs. When you abuse the free will that you have been given to harm others or to commit acts of hatred or violence instead of choosing the right path then you have the power to destroy lives instead of enriching them, but this power comes at a great price and you will have to answer for these actions in the future.
Having a choice between good and evil is something that man has and animals do not, and that sets us above other species. When you choose the wrong paths and wrong decisions in life this allows evil to foster, and even small decisions can have a big impact on the lives of others. If we did not have free will then we could not make a conscious choice to do the right thing and be a good person, our ability to choose allows us to use our free will and shows what we are truly made of on the inside. Any decision should be made after a careful consideration of how this decision will affect others. If you go through this life only concerned about what you want and you abuse your free will to reach your goals even when others are harmed then evil is the result no matter how good your intentions may have been.