Clearly, if mankind has free will - which I believe* we do - then an external God is not in control of the world. That means we can't thank or blame a God for the actions undertaken by man.
Does this mean anything goes? Yes, I believe it does, as the bloody history of mankind shows.
So where does "God" fit in to this?
Even though man has free will and can create a heaven or hell on Earth for himself and others, it doesn't mean that "God" is not working "His" purpose through the world.
How is this happening? Purely by self-conscious, free-will beings living and learning from their experience. Poor decisions harm the self and others whereas good decisions help The All to become More.
By living on earth and experimenting with his free will, man eventually learns to use that will in constructive ways after experiencing the pain of its destructive use. In this manner this earth serves the purpose of God by helping in the evolution of the soul of man. The evolution of non-human souls may also operate in a similar way with growth occurring through experience.
God/source exists, free will exists, reincarnation exists and continues until a given soul has learnt all the lesson they need from earth life.