The last icons of the past are the non-believers, whos very existence is proof that there is another valid way to believe and perceive the world; that there was an old way, and that it worked to make the civilization they wish to conquer and call their own work. Those people have to be removed or destroyed, otherwise they present an existential crisis to the believers; that they might be wrong, and that there might be another way of believing and behaving that results in civilization and prosperity.