Cofty,
Maybe I should clarify I meant what atheism sees as the biggest problem in relation to theism. I am sure you will agree the existence of evil realities is something atheists use in their preaching. Children die of starvation and so it is absurd to believe God hears prayers. So evil fates and our meditation concerning it make the existence of God impossible / absurd.
I am happy to say I have never believed in free will nor do I know what it is. God chooses, appoints, elects. Creation run its course and God intervenes. We are products of many conditions.