The trouble sometimes in arguing with theists is that they always have these get-out arguments that cannot be challenged, not because they're right exactly but because they're just... vague. "It's all part of God's plan", "That's just free will", or the killer "I don't know - but God does". How do you even argue against that? Other than by pointing out the obvious -- that these aren't arguments. Oh well.
The "Pain is all part of God's plan as a test" one has always bugged me. Why set up tests when He knows the result? Or, more accurately, why set up tests where the consequences of failure are so grim? Adam and Eve, apparently, failed the test of eating of the fruit they weren't supposed to -- and so we were cast out of Paradise. Well brilliant. Why not just not put the tree there in the first place, God?
Etc., etc.