Free will is of course impossible no matter whether christianity is true or not. However, since christians promote free will, I am having fun talking about how omnipotence and omniscience make free will sound even crazier than it does to an atheist.

Either god is in control or he is not. If God is not in control, who is? It certainly isn't us since we don't choose free from causality. If god is in control of all that happens, then no doubt god is the most successful murderer and rapist. The problem of evil as an argument against the existence(or at least the benevolence) of this god is the strongest cause for people deconverting from christianity.