How do we know who is sane or who is insane?

Ok, there are supposedly two sides, the sane and the insane. That being said, how do we know who is which, if that makes any sense. The so call sane people claim they are the sane ones, and the so call insane say the sane are the insane ones. Both sides say the other sides beliefs and views are completely insane. Is there any way of ever finding out which side is right. I mean what if the majority of people that claim to be the sane ones........are really the insane? I am considered insane by alot of people because I say that evil is neccessary in this world, especially from a christain standpoint. God wanted beings that had free will, and would worship him because they wanted to, not because they had too. The only possible way he could do that is allow good and evil to coexist. Because lets face it, you just can't have free will with only good in the world. that would mean that theres only one path to choose. And without God in the picture, the plagues and diseases, the wars, the bad times, because without bad times you wouldn't know the good times when they came around. They are all neccessary as population control, and they are sooooo neccessary to the cycle that this earth has gone thru since its first day. Except for wars, which take place cuz lets face it we humans are truely programed to destroy ourselves. Do you have any idea how over crowded the world would be if we took out all those factors. I mean we would have already used up the remainder of our already extremely limit resources a long time ago. Did you know that most of earths species will almost inevitably become extint, and they are ment to. We shouldn't mess with the natural opperation of things, its not our job to do so. Theres no telling how much we could mess up, because we know so little about everything anyway. Oh nevermind don't listen to me... I'm just a madman!