I believe the simplest explanation is, there is no God. No one created the universe and no one directs our fate. This leads me to a profound realization that there probably is no heaven and no afterlife either. We have this one life to appreciate the grand design of the universe and for that, I am extremely grateful.
And here is the point, about myself and my co-thinkers. Our belief is not a belief. Our principles are not a faith. We do not rely solely upon science and reason, because these are necessary rather than sufficient factors, but we distrust anything that contradicts science or outrages reason. We may differ on many things, but what we respect is free inquiry, openmindedness, and the pursuit of ideas for their own sake.
The God of the Old Testament is arguably the most unpleasant character in all fiction: jealous and proud of it; a petty, unjust, unforgiving control-freak; a vindictive, bloodthirsty ethnic cleanser; a misogynistic, homophobic, racist, infanticidal, genocidal, filicidal, pestilential, megalomaniacal, sadomasochistic, capriciously malevolent bully.
I was raised thinking that moral and ethical standards are universals that apply equally to everyone. And these values aren't easily compatible with the kind of religion that posits a Creator. To my way of thinking, an omnipotent being who sets up a universe in which thinking beings proliferate, grow old, and die (usually in agony, alone, and in fear) is a cosmic sadist.
For God to prove himself on demand, physically, would be a grave disappointment, and the strongest Christians should be considerably grateful that he chooses not to do so. The skeptic endlessly demands proof, yet God refuses to insult the true intelligence of man, the '6th sense', the chief quality, the acumen which distinguishes man from the rest of creation, faith.
So it is best to keep an open mind and be agnostic. At first sight that seems an unassailable position, at least in the weak sense of Pascal's wager. But on second thoughts it seems a cop-out, because the same could be said of Father Christmas and tooth fairies. There may be fairies at the bottom of the garden. There is no evidence for it, but you can't prove that there aren't any, so shouldn't we be agnostic with respect to fairies?
The only position that leaves me with no cognitive dissonance is atheism. It is not a creed. Death is certain, replacing both the siren-song of Paradise and the dread of Hell. Life on this earth, with all its mystery and beauty and pain, is then to be lived far more intensely: we stumble and get up, we are sad, confident, insecure, feel loneliness and joy and love. There is nothing more; but I want nothing more.
It means that your birth, with all your particulars, is a wildly improbable event, and hence precious. You won the sweepstakes by being born at all. Think of all the wallflower sperm and egg cells. You made it, buddy. Whew! What a staggering wonder! What a thing to rejoice in! The lottery wasn't fixed! God didn't rig it! You won fair and square! What a miracle!
If every trace of any single religion were wiped out and nothing were passed on, it would never be created exactly that way again. There might be some other nonsense in its place, but not that exact nonsense. If all of science were wiped out, it would still be true and someone would find a way to figure it all out again.