IMHO, assuming that ID is true for the moment, the nested hierarchy screams multiple designers.
What we would see as the evolutionary arms race would also be very strong evidence for a minimum of two designers. The attack and defense mechanisms are often highly complex, and only designers in competition would go to such lengths.
Either that, or a single designer that slightly modifies pre-existing species and then suffers amnesia after designing the new species.
Your "amnesia" hypothesis could cover the evidence, I suppose. The designer keeps forgetting which side of the arms race he's on.
Well If you take it from the view of similar design, it would probably make sense.
Example: if were to start my own line of designer clothes, for each garment I make I would probably leave my signature on it to symbolize that the garment was fashioned by me. It would then be natural to think that there was probably one designer or one mind behind the design upon seeing my signature left on my product.
It would? Would I assume that the fashion house whose products bear the SavageD logo only employs one designer? And would I assume that someone, perhaps called D Savage, was the original inventor/designer of all shirts, dresses and skirts, rather than being a modifier of designs made by others? Would anyone assume all this?
Similarly every living thing contains some sort of signature (eg. dna). Why does every living thing require dna, why not some other mechanism for information? Probably evidence for common design.
DNA is a working part of the organisms that contain it, not an arbitrary sign intended for observers like the trademark logo that you choose to put on your clothes. If the logo is accidentally left off a batch of dresses leaving your factory, they are none the worse for it. Leave DNA out of a life form and you would have to substitute another self-replicating molecule. Designers could easily do this, but with naturalistic common descent, it would be difficult. Hence the uniformity.
It's fine to illustrate arguments by analogy, but there's no single sign we know of in all organisms that's analogous to the SavageD trademark on your clothes. The identification signals that organisms do use to communicate with others are the nearest thing in a way, but these are many and varied. They use a whole variety of species specific chemical signals, sounds and visual displays as signs. Going by your argument, each species would have separate "trademarks", and therefore separate designers.
The biological system also exhibits an intricate system (ecosystem).
plants depend on insects & animals animals depend on insects & plants insects depend on animals & plants
Every-things intertwined, if you remove one of these, the entire ecosystem falls apart. This would then be evidence for a common designer since there was probably common thought used in designing the system.
That's the funniest version of the "irreducibly complex" argument I've ever read (and I've read a few that make me laugh). Thanks for it. It could be very useful in explaining what's wrong with the concept when people apply it in other areas.