You've missed my point (I think). I don't argue that there's no God. I agree that science cannot make any such statement. I am arguing that if there is an intelligent designer, then such a designer must have either arisen as a result of natural processes or must have always existed. In the first case, why is it more plausible that an intelligent designer arose by natural processes than it is that a single celled organism did? In the second, I would contend that an intelligent being that has always existed would be recognized as a god (not necessarily the Christian one) by most people. In the first case, ID is pretty much equivalent to abiogenesis. In the second, ID is a form of creationism.
I understood your point, but we both also understand that the "who designed the designer" questions are supposed to build up a logical chain to the "inevitable" conclusion that "there is no God."
However, the question is actually irrelevant to the question of life on Earth -- which is the only evidence we have of life in the universe, however it came to be. The unspoken assumption seems to be that there is no other possible type of life: which seems a rather presumptuous claim.
Looking at life on Earth, the bottom line is this: there's no reason for us to rule out the possibility that intelligent designers played at least some role (not necessarily an exclusive, or even a predominant role) on the way life has turned out here. The best reason for not tossing out that possibility is that we humans have been doing intelligent design for millenia.
The real issue here is not science per se, but rather the problem of underlying assumptions. The whole Evolution/Creation/ID debate hinges on certain assumptions about The Way Things Are, and at that level the discussion is almost never "scientific."