We know that specified complexity is reliably correlated with the effects of intelligence.
- William Dembski, Is Intelligent Design Testable?
Our experience-based knowledge of information-flow confirms that systems with large amounts of specified complexity (especially codes and languages) invariably originate from an intelligent source from a mind or personal agent. As Quastler (1964) put it, the “creation of new information is habitually associated with conscious activity” (p. 16). Experience teaches this obvious truth.
- Stephen C. Meyer, The origin of biological information
But an equally obvious truth goes unmentioned: Experience also confirms that intelligent agency invariably originates from complex mechanisms.
Everything we know of that is capable of exhibiting intelligent behavior is a physical system containing "high levels of specified complexity". A computer can behave intelligently, but not without the functioning of its complex electronic machinery. Likewise, the computer programmer behaves intelligently, but this requires the functioning of another complex mechanism - a biological brain. Scientists have learned a great deal about the neurological mechanisms that enable our perception and reasoning abilities, and while some people believe that something in addition to brain processes may be involved, our experience confirms that without a functioning brain, nobody can design anything at all.
So if there is evidence to confirm that mechanism does not arise without mind, as ID proponents claim, then that very same evidence also confirms there is no mind without mechanism. And if mind can't exist without complex mechanism, then the original complex mechanisms cannot have been the product of mind.
Of course we can imagine that some sort of mind somehow came to exist independently of mechanism, and that it could somehow interact with matter in order to create the first living things, or even the universe itself. But while we can imagine such things, in our experience all minds are necessarily associated with complex physical mechanisms. It is no more consistent with our experience to postulate the existence of an immaterial intelligence than it is to postulate complex mechanisms arising without intelligent agency.
Faced with this obvious and fatal contradiction to the claim that ID is based on the facts of our experience, ID enthusiasts will point out that they don't actually say that the Intelligent Designer is supposed to be a spiritual, disembodied entity; they explicitly allow for the possibility that an extra-terrestrial life form may have been responsible for designing life on Earth. This seems to be a disingenuous ploy, however: Once we posit the existence of extra-terrestrial life, the most straightforward conclusion would be that the species of Earth are simply the descendants of these alien life forms, rather than the products of some sort of advanced bioengineering efforts.
In any case, speculations about extra-terrestrials being the ancestors (or the architects) of life on Earth have been around a long time, suggested by Francis Crick, the Raelians, and others. These ideas have generated relatively little interest over the years, mainly because there is no evidence that they are true. But even if we somehow discovered that we did come from alien life, we still would only be explaining how life forms came to planet Earth from elsewhere, rather than how life forms ever came to exist in the first place.
If ID attempts to explain the origin of life in the first place, then ID's "intelligent designer" must be some kind of mind that exists without the benefit of a living body. While it's true that many people believe in ghosts, fairies, gods, devils, demons, or other immaterial (or at least non-biological) entities with minds, there are also many people who do not believe in such things. Clearly if there was any scientific evidence of paranormal or supernatural phenomena like these it would be tremendously important for ID, so one might think this issue would figure prominently in ID "research". For whatever reason, however, ID authors seem disinterested in providing evidence for the existence of intelligence that does not arise from a complex physical mechanism.
So it turns out that ID proponents are mistaken to think that experience-based knowledge supports the idea that something consciously designed the universe or the first living things. On the contrary, our experience-based knowledge of intelligent agents suggests that nothing without a complex body could have a mind at all, which in turn implies that there could not have been any conscious designers of anything until advanced life forms had already come into existence.
Nobody can be sure that we will eventually account for the origin of life in terms of physics and chemistry, but if we do manage it, the processes involved will have to be confirmed by the observations of independent researchers. Likewise, evolutionary biology attempts to explain the origin of the species by reference to things that we can all experience through observation - variation, heritability, differential reproduction, and so on.
As far as our experience goes, however, conscious minds require living brains, so imagining that living things were designed by a conscious mind is like imagining someone pulling themselves up by their own bootstraps. Maybe it could happen, but it's very much at odds with our experience.