So why is the design inference sometimes permissable and other times not permissable? The answer appears to be in Alexander’s caricature of design theory. He writes that many IDs:
believe that only through the gaps in our present knowledge do we have incontrovertible evidence that God is at work in design. 
Alexander gives no citations of examples of IDs holding so to such a belief. Is there a single mainstream ID proponent who has ever promoted this notion?