Really, really old models of Adamic origins

Young Earth Creationist (YEC) thinkers believe most if not all species in the Homo genus comprise the species of Adam (e.g. here, here, but see a contrasting view here), and at least some Intelligent Design proponents seem to agree (see the chapter on human fossils here). These are the arguments for and against for such a position:

For:

Adam and his descendants need to be completely different from anything that came before them, not just in terms of cognitive capacities but also anatomy. Even the earliest members of the Homo genus have a suite of anatomical features that look completely different from the ape-like creatures that existed before them. Furthermore, different species with the Homo genus differ only slightly. As such, the genus seems to comprise a tightly similar unit of human-like creatures that are unlike anything that came before, which respects the traditional intuition about human uniqueness. The YEC Marvin Lubenow in his Bones of Contention argued as such, so did ID theorist Casey Luskin in his chapter in the Science and Human Origins. Perhaps the most sophisticated defense of the view comes from the YEC Todd Wood, who claims to demonstrate evidence of "biological discontinuity" between Homo and non-Homo species based on a trait-based clustering method (see some of his latest stuff here, and responses to criticisms here). Wood claims his analysis is compelling and robust, since they reveal the same pattern of clustering regardless of which fossil trait datasets or statistical tools are used.

Against:

Humanness necessitates two things - human-like cognitive abilities, and anatomical similarities. The further back we place Adam, the more difficult it gets to defend the idea that his earliest descendants demonstrated cognitive capacities found in modern humans. Not unsuccessful, to be sure, but difficult. Similarly, the more different Adam and his earlier descendants look from us, the harder it becomes to say that they were humans.

Personally, I'm more sensitive to the arguments against this model than the ones in favor of it. For example, Ian Tattersall claims the definition of Homo is a vestige of old-time taxonomy, where systematists felt the need to place everything in either the Australopithecus basket or the Homo one. If that is true, it becomes more contentious to claim that the earliest members of the Homo genus would have anything to do with modern humans.

Maybe a more direct disproof of this view would come from the anthropological research conducted by Gregory Forth who, based on his analysis of testimonies given by indigenous people of Flores, comes to the remarkable conclusion that Homo floriensis are either still alive, or were alive until recently (book, interview). For our purposes, the relevant bit of his research is that the people of Flores almost unequivocally classify these creatures as being non-human. I think that testimony is really powerful, since probably the most compelling criteria of humanness is I know it when I see it.

I'm curious why, despite such potential problems with this model, it continues to be popular. I suspect the most recent book on YEC paleontology also argues for this view.

Maybe it's because the argument for the view - the necessity for biological discontinuity - is seen to be a far more powerful consideration than those against. After all, it's probably difficult to show that earliest hominins did not have modern-type cognition. One of these days I want to do a thorough investigation of the model.