Ignorance of an enemy works well for those which desire most for that enemy to be destroyed. It is far easier to destroy something faceless, that possesses no humanity and can be labeled as a monster or unnatural; than it is to face someone that you know likely has people they care about in some manner and is possibly just as human as you are in the ways in which it matters most to you.

People will believe what they desire to believe, no matter how much evidence you may give them to the contrary. Some refuse to acknowledge the world is not as simple, black and white, cut and dry as they desire it to be. Some things can not exist without others, because if they did, they would then lose what meaning they once held.