"Now, that said, let me ask: is there any epistemic value in the concept of common design other than co-opt evidence for evolution?"
i) This is a beautifully anachronistic statement of the issue. The concept of common design doesn't "co-opt" evidence for evolution. For one thing, the concept of common design goes back to the Judeo-Christian concept of divine creation, which antedates the evolutionary debate by centuries and millennia.
All I've done is to apply a traditional teaching to a new issue.
ii) In addition, to say it's co-opting the evidence for evolution begs the question of whether the evidence singles out evolution.
"I think there is not. In practice, the invocation of common design is clear in its utility; as Steve Hays says, why can’t any evidence for common descent simply be evidence for common design? The answer is… it can!"
Which is why the evidence for common descent is not, in fact, evidence for common descent. It's consistent with common decent, but it's consistent with common design. At that level, both explanations are empirically equivalent.
"And that’s precisely the problem. Common design is an infallible, unfalsifiable hypothesis, even in principle, and therefore useless scientifically."
Several more problems:
i) Science is not the sole gateway of truth.
ii) Not all truth is hypothetical.
iii) Why assume that reality is always engineered for the convenience of a scientist? Indeed, that would be a design concept.
"The natural response would be: Ok, what would be evidence that doesn’t support common design? Obviously, not all creatures are exactly alike, so common design allows for differentiation and specialization. What then, would argue against common design as an “explanation” for observed similiarities, functional or no? I don’t see that common design could possible be discounted; it can account for anything, as it invokes an unidentified but infinitely capable Designer."
i) The concept of design antedates ID-theory. And the Judeo-Christian concept of creation does not invoke an "unidentified" Designer.
ii) But suppose this were a debate over ID-theory. T-stone's problem is that because he's a dogmatic theistic evolutionist, he can't even stand the watered-down theism of ID-theory. And that's because some, but not all, ID-theorists are opposed to evolution.
"Such is the poverty of ad-hoc creationism."
The traditional, Judeo-Christian doctrine of divine creation is "ad hoc"?
"If you’re undisciplined in you epistemology, “Goddidit” becomes a reflex, and especially useful as a dismissive defensive weapon."
Notice how t-stone, who poses as a Christian, never takes into consideration the possibility that there are times when, in fact, "Goddidit" is the correct answer. He's a functional atheist.
He doesn't ask, "What is true?" but only "What is scientific?"
He'd rather believe something that's "scientific," but false over something that's true, but "unscientific."
"Vitamin C deficiencies shared across primates? No problem, it’s easily explained by common design, much easier than by common descent, by the way. Homologies? Evidence of common design, just like any other similarities you can name!"
Notice, once again, that he never allows himself to entertain the possibility that even some commonalities might be due to common design. As I say, he's a functional atheist.
Although he poses as a Christian, he regards it as utterly illicit for a Christian to ask himself: "If there is a Creator who designed the world and brought it into being, then what would such a world look like?"
To him, a Christian must never begin with revealed truths.
Instead, a Christian must act as if there is no God, as if we inhabit a godless universe. That's the only "scientific" way of doing science.
"We might suppose we have fine grained transitional evidence for evolving morphology and constitution from one species into a markedly different species."
Except that we don't.
"Would that be enough? No, because every evolved step in the sequence can be accounted for by an intervening miracle, a bit of special creation on God’s part rather than the product of variation and natural processes."
He erects a straw man argument to burn it down.
Incidentally, special creation doesn't disallow natural variations. That's another straw man argument.
"Is it wrong, then, to invoke the idea of 'common design in scientific inquiries like this?"
i) He's assuming that this can only be a "scientific" inquiry.
ii) And he defines science in systematically atheistic terms.
"I won’t say it’s wrong, but I will say that brings the inquiry to a stop in terms of science."
No, just the opposite. If you think something was designed, then that encourages you to look for an explanation rather than treat it as a brute fact or surd event. Belief in design is an impetus to scientific discovery. You only seek a rational explanation if you believe that a rational explanation is available, which assumes the rationality of nature.
"If common design is the reason for the similarities, than science can’t hope to account for them by natural mechanisms; the isomorphisms as the product of arbitrary intelligence, and thus beyond the ken of science."
So the mind of God is equivalent to "arbitrary intelligence."
"Steve Hays can wave away the compelling evidence for our common ancestry"
If, according to t-stone, common descent and common design are empirically equivalent, then there is no compelling evidence for common ancestry. Indeed, by his own admission, there would not even be any *distinctive* evidence for common descent, much less *compelling* evidence.
"In that respect, common design is a recapitulation of the idea of “mature creation” that YECs have adopted in response to the lopsided scientific evidence against their beliefs."
Yet another anachronism. Belief in mature creation was not adopted in response to modern science. This is simply an application of a traditional belief to a modern issue.
"Sure, the universe looks old, but God just created it to look and act billions of years ago, even though He created it all just a few thousand years ago."
i) As I've said before, the universe doesn't look any particular age.
ii) As I've also said before, a theistic evolutionist like t-stone believes quite passionately in a gap between appearance and reality as far as the age of the universe is concerned, only—for him—it's in the opposite direction.
For him, stars look younger than they really are, rather than older than they really are.
"Forced into a bind by the evidence for common descent, creationists invoke common design in the same way they invoked the idea of 'mature creation' when vexed by the overwhelming evidence for an old earth and universe."
i) But if, by his own admission, mature creation is empirically equivalent to the alternative theories of establishment science, then there is no "overwhelming" evidence for an old earth and universe. Indeed, there's no *distinctive* evidence for either.
ii) What t-stone does is to equate achronometic, natural processes with chronometric, artifactual processes, in a completely anthropomorphic fashion.
In t-stone's preschool universe, a rooster exists to tell us the time. And if the rooster doesn't wake him up in time for work, then God is a fraud.
"But they are both the epitome of the ad-hoc “just so” story, appealing to God’s plenary powers as a way out of the evidential vise they are in."
If you want examples of ad hocery, study the many versions of cosmology and evolutionary biology.