Can you blame them though? It's not any clearer than mud that God exists, it's not any clearer than mud of what morals one should have, and if you decide to have both, it's not quite clear.
Perhaps if God didn't separate them from himself their actions would have changed to something better.
A complete turning away from God is not just simple atheism. It's giving one's self over to all that is opposed to what is holy - hatred, violence, anger, greed, lust, pride and other things such as despair and nihilism when the person does not even attempt to find meaning or hope. What separates us from God are all the things that violate virtues such as charity, hope, mercy, compassion and forgiveness. There can exist atheists who are still searching for God in the way that they know how to do but don't think they've found Him, yet still leave the door open to Him.
If freewill exists in heaven, then evil exists in heaven. If evil doesn't exist in heaven, then evil is no longer a choice and thus freewill is tossed out like trash.
What a weird notion that you seemed to have made up yourself. No evil can exist in Heaven as nothing impure can exist in God's Kingdom. That's why when the rebel angels rebelled, they were cast out of Heaven.