A few assumptions I see being made:-
Atheism = Lack of belief in a theistic god. A theistic god is a specific definition of god. (Basically a super-human)
Everything does not need an explanation (necessarily). The simple fact is, try to explain 'everything' and any concept you conjure fits into the category of 'everything', thus you have not given it an outside cause, thus have not explained it. It seems logically impossible to explain everything.
I think most people are agnostic to some degree, seeing as how most agnosticism contradicts neither atheism nor theism.
Finally, my views on the matter of theism:-
Theism, to me, implies the existence of a intelligent god, with a will and a purpose.
Now, my observations have not led me to the conclusion that humans contain no immaterial substance. However, intelligence, will, and purpose, I have concluded, are all material substances.
Intelligence seems explainable via our brains. In simple terms, destroy the brain, destroy intelligence. Will follows the same path. Purpose, however, simply means destination. To say 'I have a purpose', is to say 'I have a destination'. It's a specific goal to reach.
I have yet to encounter anything that does not have a purpose, in that sense.
By this definition, evolution is intelligent (how is it different from our own intelligence?), it has a will (how is it different from our own wills?), and it has a purpose (as does everything).
The same can be said about the observed universe. It created us, it nurtures us, and it has a purpose. I'm not anthropomorphizing the universe, other people anthropomorphize humans. A rock 'wants' to be in the centre of the earth the same way a human 'wants' money, one is no different from the other. Humans are simply harder to understand than gravity's effect on rocks, from a human POV anyway.
I guess you could say the universe is omniscient (it certainly contains more knowledge than any human), certainly omnipresent, but only omnipotent if one defines omnipotence as being capable of all that is logically possible (the only sensible definition). Benevolent? I can't even begin to imagine the workings of a benevolent mind. Afterall, an omnipotent being by the definition I stated, might need to cause suffering in order to be benevolent. So on that matter I don't know.
However, who's to say what is outside the universe? Thus, ultimately, scepticism wins. Theism, in the sense I have presented it, seems quite rational though.