For some reason I've been doing a bit of tilting at windmills, posting comments to a couple of discussions of biblical history here. Really, it is hard to know where to begin with people who have such strange standards of evidence. In the present instance, of course, there is also their apparent blindness to how non-standard their treatment of ancient source material is, and to how differently they treat pro-Christian vs. other sources.
Of course, there may be an element of deceit, or at least indifference to truth; I admit I find it very hard to resist such suspicion in the case of Lydia McGrew. But there are less extreme and more respectable biblical scholars who nonetheless share unusual standards of evidence. Thus, I think it's worthwhile to ask why such unusual standards of evidence are inappropriate.
Obviously, the argument cannot be any appeal to authority, and in the present context any very direct appeal to the success of more orthodox historical standards is likely to be little more than that, as our main measure of success in investigating history is producing results acceptable to orthodox historians. Nor is it the case that the advantages of one kind of approach to evidence over another are obvious in this area. There is certainly no canonical list of acceptable evidence and appropriate evidence weights to consult to decide such issues; indeed, discovering new kinds of evidence and new ways of looking at things is one of the most important engines of intellectual progress.
I think the analogy of science is instructive. Kuhn is especially famous for having noted the evolving nature of standards and evidence in science; a Kuhnian paradigm is so-called because it centrally involves paradigm cases of observation and measurement, paradigms of evidence gathering and evaluation. If Kuhn were right in the extreme claims he sometimes made that choice of paradigms was subjective, irrational, and independent of evidence, then it would be hard to criticize the biblical historians for adopting the approaches they do. But Kuhn was not right about that. Though the standards for evaluating paradigms are different from the standards of evidence evaluation internal to paradigms, they are not automatically irrational.
One of the most important such standards is fit with other successful theories. It is for this reason that I am an advocate of reductionism and unity of science ideals generally; reductionism is a quest to find the logical relations between theories, so that inconsistencies can be exposed, since inconsistencies show, as always, that there are problems somewhere.
This is a basic problem for the paradigm employed by those like McGrew; one of the more easily described features of the paradigm is that reports of miracles in ancient sources are regarded as comparable to other kinds of reports in ancient sources. A paradigm which treats those different kinds of reports as equivalent does not fit with our scientific theories (a point made by Hume, of course). Thus, the standard paradigms employed by mainstream ancient historians, paradigms which give no weight to the possibility that miraculous reports are accurate (and for that matter lower than usual credence to the possibility that they are distortions of actual events and higher than usual credence to the possibility that what they report has no similarity to anything that actually happened) are better than the paradigm employed by McGrew.
I am not entirely certain what her view of these matters is. Sometimes she writes as if she thinks it's an unreasonable bias to expect historical claims to be scientifically plausible. It is hard to know how to respond to that. Oddly, she and her allies do sometimes write as if theological soundness is relevant to evaluating historical claims; this seems to be a recognition that fit with external theories is important, though of course theological paradigms do not fit well with successful scientific theories either (nor do they show any of the other usual marks of successful paradigms). But sometimes she writes as if she thinks she's just using obvious standards, or as if she's using the same standards as ancient historians use generally. If that is truly what she believes, it is again not easy to know how to respond to such an extraordinary view.