I don't want to start a religious debate, but I do want to say one thing. Ultimately, proper scientific method applied to the existence of God or some kind of divinity fails to disprove said existence, and therefore the theory of a God existing holds true, while the opposite is also true, meaning the theory of no God also holds true. Both theories are founded purely in belief and faith, and so atheism is effectively a religion. Agnosticism is the one viewpoint that can truly be counted as non-religious, as an agnostic doesn't believe or care either way. Now, I'm not saying any one view is superior or inferior, merely that there are far too many closed minds due to religious beliefs. And, for the record, I do believe in God, but I also hold to the knowledge that the Bible was written by man, and therefore cannot be held to a literal standard or view, and anyone who does is setting themselves up to sound like total crackpots, whatever view they hold, including atheistic.
Cancer, baby diseases, and a lot of disgusting stuff exists and happens all over the world.
You're right that this doesn't necessarily proves that God doesn't exist. The reason why babies can be born with nasty conditions even if their parents take all the cares in the world may just be because God willed it.
It however proves that if God does exist, then he/she/it has a very sick sense of humor and/or extreme cruelty, and the only reason to worship him/her/it is out of pure fear so that he won't smite you down or your descendants with horrible diseases. Except he/she/it'll then randomly smite you or your descendants with horrible diseases now and then.
Also as someone once pointed out, what kind of "intelligent" designer puts your natural recreation center just next to your natural waste disposal system? It's kinda laughable when you think about it, and thus on-topic for this thread.
tl:dr: If God does exist, he makes most RPG authors look like freaking design genius by comparison.