Supposedly, bad design is a refutation of intelligent design. How is bad design and intelligent design compatible? This is one of the most common arguments raised against intelligent design, albeit one of the more egregious ones. The argument goes like this: an intelligent designer would not have designed biological system X in this way, therefore Darwinian evolution dunnit.
I think one of the first things Darwinians need to learn when attacking intelligent design is exactly what it posits. Intelligent design, as a scientific proposition, holds that certain features of the biological world are more adequately explained by an intelligence rather than a mindless process.
So, we hold that only certain features in biology are more adequately explained by an intelligence. This alone is sufficient to overturn this argument against intelligent design. But what about flaws in the design of systems that are purported to be intelligently designed, such as the flagellum? First off, bad design is seen in objects that humans design. A broken down, badly-running watch does not indicate that it is not intelligently designed.Maybe the designer(s) of biological system X was having a bad day, and "it" made an error in designing that biological machine.
Now we come to the philosophical argument from bad design: namely, that bad design proves that the designer was not God. Proponents of this argument ask, "If God is perfect, then how could a perfect God made a bad design?"
P1: God is perfect, and humans are not perfect. God is omnipotent, and you are not.
P2: An imperfect, non-omnipotent being is incapable of discerning poor designs of a perfect, omnipotent Being.
P3: Therefore, we cannot assert that the design of a perfect Being is imperfect, for we are not omnipotent.
I am expecting a response like "that's just special pleading" or "you are using the God-works-in-mysterious-ways argument." Obviously, these responses are only appeals to emotion, as they do not attack any of the premises in the above argument.