Leave it to Davescot to find a way to wad up several ID fallacies into one, quivering little article.
In it he plays the game of claiming that scientists treat ID as both falsifiable and nonfalsifiable at the same time, justifying this with [sigh] a quote from Charles Darwin:
"ID is ineligible for consideration as science because theories that allow for the possibility of forces outside of nature can’t be tested or falsified.
In light of that let’s look at what Ernst Mayr had to say in the introduction that appears in “Origin of Species”, Harvard University Press edition, 1964, p. xii:
In Darwin’s day the prevailing explanation for organic diversity was the story of creation in Genesis. Darwin himself had subscribed to this when he shipped on the ‘Beagle,’ and he was converted to his new ideas only after he had made numerous observations that were to him quite incompatible with creation. He felt strongly that he must establish this point decisively before his readers would be willing to listen to the evolutionary interpretation. Again and again, he describes phenomena that do not fit the creation theory.
Huh. It appears like Darwin was testing scientific creationism and found evidence contrary to it.
So what is it. Is ID science or not science? It seems our opponents want to have their cake and eat it too by saying:
“ID is not science because it cannot be falsified or verified. And by the way, ID has been repeatedly tested and shown to be false.”
Where to start. In the first place, evolutionary science is not an authoritarian philosophy like religions are. It is not now, nor has it ever been, reliant on what Charles Darwin said. We have learned a great many things biological in the last 150 years, especially little things like DNA and genetics. To represent current scientific theory by what Darwin said is ignorant in the extreme. Darwin would be astonished at what his writings have spawned.
More generally, it is highly inappropriate to quote anyone who lived hundreds of years ago to support a position on modern theories that did not exist in their current form when that person wrote. Isaac Newton, Albert Einstein, and others who the anti-evolutionists try to coopt to their side, were creatures of their era as we all are. To assume their views would be identical were they to live today is absurd in the extreme. There was no ID formally when Darwin lived, so nothing he could have said has any bearing on what ID opponents are doing now.
As to what ID opponents do now, it is not contradictory. ID theory is nonfalsifiable, because one cannot make a prediction from "someone did something sometime". This makes sense, because ID was developed as a political strategy to get creationism past the courts. To do this, they stripped it of its content and its overt references to gods. The creationism Darwin was criticizing was science, albeit bad science, because it made many predictions that were (and are) easily refuted.
Now on occasion ID proponents like Michael Behe will make falsifiable claims, such as the claim that the bacterial flagellum is "irreducibly complex", meaning it could not be created in a step-by-step functional manner, and that if any part of it were removed, it would not function. However, the type-III secretion system is a subset (ie is missing many parts) of the flagellum, thus refuting Behe's claim. However, since there is nothing in ID theory that says "flagellum shall be irreducibly complex", this refutation of Behe's claim does not refute ID.
It is wise to watch for these subtle semantic games when dealing with ID proponents. What constitutes ID, and the criticisms of it, will shift to and fro depending on their rhetorical needs.