So, God has a specific purpose that requires sin to take effect? Some sins, or all sin? Or would this be complicity? Is knowing what will be participating in what will be? Who's to say what is not demonic where there's evil? How can you determine this?
If I had to bet on two world systems, one where man would be on his own, the other where he would be assisted by Satan and demons, until it's a whole world system that revolves around senseless, destructive sin, as in now, I'd bet on the former being a better place. Who was in the Garden, promoting sin? Again, a clear distillation of the problems,
Ephesians 6:12 For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places.
But, I assure, God is not up to promoting sin, that grace may abound.