Many atheists don't believe in god in much the same way you don't believe in ghosts or the tooth fairy or santa claus. Do you think it is intellectually honest to say that since I cannot prove that santa doesn't exist I should say I don't know? The complete lack of any evidence for a fairy tale is considered sufficient to dismiss it, why not the fairy tale of theism too?
That's just a "straw man" argument. I mean Einstein was a theist (along the lines of Spinoza's ideas) so it's not a totally irrational position to me.
I think most Atheists would certainly be open to the possiblity of such a being if evidence were to emmerge.
That seems like a reasonable position.