Why didn't god just design the world to have freewill, but to be without sin forever?

You're being way too logical. Myths like heaven, hell, gods, and saviors don't make sense -- especially when viewed in the light of the evidence of reality.

The world doesn't have sin because of our free will. The world has sin because of satan and his minions trying to pull us away from God and blinding people to what they are doing, desensitizing people and tricking them into thinking that what they do isn't so bad after all. What shocked people ten years ago doesn't shock anyone now.

There will be no sin in Heaven. There isn't any in there now.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.