I have a question for you. What do you do when there is an evil you cannot defeat by just means? Do you stain your hands with evil to destroy evil, or do you remain steadfastly just and righteous even if it means surrendering to evil?
Please note *religious answer* There is no such thing as perfection in us humans and their is evil within all of us anyway. So getting a bit more evil to defeat evil is alright.
God permits, at times, the devils to assail us, that we might turn to Him in prayer, with a renewed trust in His love and concern for us. The extraordinary priest St John Vianney, who's straw bed the devil tried to burn when he was sleeping in it, once remarked that "the devil is like a dog on a chain. He can only go so far as God permits."