Creationists and IDers may resist using religious arguments against evolution because they recognize their circular nature and that others will reject them, so they seek to attack the physical evidence for evolution itself. But it is the religious argument that motivates them completely. They know natural selection must be incorrect, so the evidence contradicting it must turn up eventually.

They wish to come up with evidence that evolution is wrong that would even convince an atheist. But their motivation is always religious, they cannot properly evaluate or interpret facts outside this mind-set. To them, evolution is not wrong because of mistaken ideas about fossils, or geological misconceptions by scientists, but because it would lead to a godless world that they cannot tolerate, or even imagine.

Religious individuals who do not reject natural selection have no problem accepting the conventional scientific evidence because it does not threaten their philosophical preconceptions. Their lack of ideology makes it possible for them to think clearly.

Creationists cannot abide evolution because it contradicts the literal infallibility of Scripture. Full stop. That is what this is all about. Without that, their entire universe dissolves into a tissue of lies. People who do not insist on literal infallibility, even though they may be otherwise very religious, have no problem accepting Darwinism. A survey of the personalities involved would confirm this. How many individuals who do not require the infallibility of scripture to support their religious beliefs reject natural selection out of hand? Without the ideological commitment, the intransigence goes away.

For argument's sake, let's postulate that natural selection is completely wrong, that some other non-supernatural, purely physical or chemical mechanism creates the changing diversity of the biological world. And let us assume that we succeed in proving it by methods acceptable to science, and that scientists are convinced by these proofs. Darwinism is discredited and a new theory takes over. Don't laugh, this sort of paradigm shift happens frequently in science! The creationist/IDers would not accept this new theory either, regardless of the evidence available for it. They are not trying to disprove Darwin, they are trying to preserve Genesis. They can never be satisfied, regardless of the evidence, and that is not science. You simply cannot reason with these people.

They aren't just convinced they're right, they're convinced they can't be wrong. There is a difference.