This is likely to be brief as I don’t think I have the cognitive ability to do a 10-page discussion at the moment, but I don’t particularly like the “This [organ, system, organism] is badly designed, hence there is no designer (and if there was he was surely incompetant)” argument. While this can lead to some interesting discussion over the how certain organs or systems are put together and were evolved, focusing on the “good design, bad design” aspect isn’t very fruitful and will likely hurt those arguing for evolution in the end. Arguing that something was badly designed takes the question out of the scientific realm and into the philosophical/theological realm (Was there a designer? When was the structure designed/created? How was it done? What was the intention?), creationists ultimately saying that God could’ve done things anyway he wanted, or that when an engineer is designing something he has to take into account space requirements, end-use, output, input, etc. Hence, they argue that organs like the eye really are well designed because they function well for what they have to do given the amount of space they have to do it.
I’m all for discussing how organs, systems, organisms, populations, etc. work and have evolved, but arguing whether something is badly designed or not, to me, seems to open the door a crack for the creationists to jam their foot in. There’s nothing scientific about arguing bad design, and while some may view it as a good rhetorical tactic, it doesn’t seem to be especially effective or convincing, and may even have the potential to backfire. If we’re going to contemplate a designer and their intention, we need a lot more information unavailable through nature (and possibly unavailable at all), so the argument for and against “good design” is fruitless, the only real benefit I’ve gotten from reading such arguments being how the eye works, how it evolved, etc. Arguing for “bad design” is almost giving creationists an allowance as it’s stepping outside of science into more abstract (and probably unknowable) realms of thought where absolute truth is more like a bluff than something tangible, hence I believe scientists would do well to abandon the argument for bad design.
Thinking about this a little further, when the “bad design” argument is used, is it really about evolution or is it about the existence of a designer? It seems to me that often it’s not so much about evolution being a reality as the non-existence of a designer. In this respect it’s difficult to separate arguments for atheism from arguments for evolution, and if we are to contemplate “bad design” it should be in terms of how evolution has shaped organisms and extinction rather than the plausibility of a designer, however incompetant.