The key word here is "seems". There's nothing dogmatic about "ruling out" the possibility of something for which there is no proof whatsoever; there's nothing there to "rule out". People have believed in astrology for longer than they have a monotheistic god; are you agnostic with respect to this as well? By your logic we cannot reject as possible the existence of dragons, centaurs, Mr. Mxyzpltk, +2 cloaks of invisibility or heads on a pillow either.
Depends on the level of ridiculousness I guess. To you, a monotheistic god, astrology, and +2 invisibility cloaks are on the same level of ridiculousness(which I'm inclined to believe as well). Whereas most people would disagree. I do not belief in god, just as do not belief in dragons or centaurs. Like I said, I really think this was some sort of biological accident. If you look at the origins of Earth, there is no way a reasonable person could say it was created with the intent of harboring life, let alone intelligent life. The earth's surface resembled that of Venus. Then, in a process that took about 2 billion years water vapor caught into the earth's atmosphere and a couple layers of atmosphere burned off. Plant life eventually developed and life started from there. I'm sure I'm missing a lot of details, just as I'm sure you probably know the story. It is highly unlikely that an intelligent god consciously made that 4 billion year process happen with the snap of his fingers in just 6 days. But can I prove it? Of course not.
I consider myself an agnostic because I simply believe there is no way we can know. Whether a god did it, a strong energy force, a biological accident, or Harry Potter conjured it all up with his wand. There is little to no proof available. Maybe my logic is flawed, but I think matters like this all logic is flawed in some way or another. That's why there are so many different belief systems out there. How do you explain the unexplainable?
Just look at Preacher. He seems to be a very smart guy, just as you do. But you both have very different views on this subject. And both of you believe beyond a shadow of a doubt that you're both right. So who actually is right? Who fucking knows?