Rational people should be agnostic. There is no way for us to know – with our limited human capacity – if there is a "god" or not. And even if there is a "god", then how do you define it?
I certainly don't believe in religion, but that doesn't mean I rule out the exitence of a truly omnipotent being. Even if that "being" is the entire multiverse and everything in it.
After all, we are all made up of individual cells, more than half of which are not even "human" (meaning they can survive on their own outside our bodies), so in every respect we are a multi-lifeform made up of many individuals.
It's not a stretch to think that we, ourselves, make up a muti-lifeform that is far bigger than our own comprehension. Hence I'm agnostic, not athiest.