I think it is like this: we can even find a flaw in the most exquisitely designed machine, or a most aesthetically pleasing painting. Just because things dont fit in with what we consider ideal, it does not mean things are not ideal. Blind spot is due to optic disc and optic nerve in our eye seems to be in quite an ideal location, very close to fovea (less distance to travel for action potentials in axons before entering the nerve). For one argument against intelligent design, we can bring 10 which show how optic nerve is in ideal location.