You can only assume there is a God, if you assume that he's a giant asshole. I mean:
1) He's still mad because of that damn apple.
2) He constantly wants to test us and he'll do everything in his power to make life more difficult.
3) If your life sucked and you weren't happy about it sucking, the afterlife will suck as well. You're supposed to suffer with a smile.
4) He creates utter chaos by letting people invent other religions. It's impossible to know what you have to do to get to heaven, it's all a game of chance really. So once again, you might be fucked.
5) He wants us to mutilate our genitals.
Sounds more like The Joker to me.