BlaSPHEMY apart... This is so tricky. In fact as tricky as quantum physics. Yeah you can tell me all about quarks but if you don't fully explain it and explain to me as has been explained, it is all guess to me.
Same with the idea of a God. The idea of His existence is ancient, billions of people took that for granted, as I do, and unless "I've" been proven wrong, he exists.
May well be all started with a guy, who knew the cycles of the earth and sun, who was able to "predict" when is going to rain, that used this for a means of control based upon divine. This being the case he himself could then declare his "divinity", rater than choose a divine being to take the credits for his knowledge.
I choose to believe in a bigger presence than myself. His existence can't be proven, can't be measured, can't be weighted. But just like with blind love, or love at first sight, I choose to believe in this.
I find that this believe helps me to keep myself in check, not going all supreme and righteous on my fellow human brothers. This I think is the most useful aspect of God in our society. Balance.
Now, have this been used throughout the ages to control people? Yes.
Doesn't mean I'll invalidate the core ideal because of the manipulations of people that came after the idea itself. Making an analogy, just like with communism. The manifesto is good, and in it's nature righteous, just like Bla said. All the countries that used this manifesto usurped these ideals, and it doesn't invalidate the idea of communism itself, is still a good idea.
Same with God. Good idea, and the nefarious behavior of the people that usurped this idea won't make me stop thinking that the idea is good.