Often, the desire to "rid the world of evil-doers" reflects a prideful mindset that creates more evil through an uncritical crusade. The more we try to control things, the more they get out of hand. This is a truism that we see not only in Scripture, but in literature from ancient to contemporary times. We must recognize that, ultimately, only God can put an end to evil. To think otherwise is to place an eschatological burden on ourselves or on society that it simply cannot bear.
So can we do something? Yes, of course. But can we prevent evil from occurring again? No, and the more desperately we try to prevent others from doing evil, the more we ourselves will become the very thing we fear.