Counterfactual speculations of the kind that Lewis is trading in are in any case airy and insubstantial because we lack the knowledge required to evaluate them.
Goodness knows I engage in a bit of "counterfactual speculation" in my own book, but that review hints, I think, at one of the unfortunate realities of pop-history: that these books are much easier to market when they include a provocative thesis that can be used as a bludgeon by one side or the other in the culture wars. I won't claim to be unbiased, of course, but I will claim not to have an agenda. I just want to tell a good story that reminds readers that iconic historical figures were fallible and imprescient human beings, a realization that hopefully will make those readers think more carefully before they enlist historical figures in modern political debates. Hmm--perhaps I have an agenda after all.
No, I don't think you have an agenda, Jeff. What you say is what I think historians are supposed to do: Tell us as best they can what happened in the past. The past, in fact, is not a gloss on the present, tendentious types like Lewis notwithstanding.