Niall Ferguson is a historian who thinks there is some worth in working through counterfactuals.
Counterfactuals, alternate histories, ("What if the South won the Civil War? What if JFK had not been assassinated? What if Napoleon had won in Russia?" etc.) have had quite an extensive fictional treatment.
Ferguson's counterfactual analysis, from a historical standpoint, is less about a "what if?" story, and more an examination of the context and contingency of historical events, and the role that people - and luck - play in them. "For want of a nail...the kingdom was lost", etc.
The deceased biologist and popular science writer Stephen Jay Gould wrote several treatments about this with respect to Nature. His views of contingency and determinism lead him to the statement that if: "You could rewind the tape of Life, it would never play the same way twice".
I think the technique is not without merit, and no doubt history is neither fixed nor inevitable, but the one thing that is not covered in these thought experiments is, not what would happen afterwards, but what would it take to get there?
I recently had a discussion in which the question "What if Hitler's labor camps were just that?" Labor camps, not extermination camps, but camps as portrayed in their propaganda? And the consensus was that Germany would obviously still have lost the war, but wouldn't have had to deal with the Holocaust, and the obvious eternal stigma. Israel most likely would not exist. Perhaps European governments, in reacting as they did to right-wing totalitarianism, may not have been as socialist.
But I thought of a more interesting question for this counterfactual, which was, "How could you even get to that situation?" I've asked this question before when the subject of "What would it have been like if the South won the Civil War?" (Let me get back to that in a minute).
How could Hitler and the Reich possibly have set up camps that did not exterminate Jews? And I would suggest that among the likely requirements for this to occur would be that Hitler could not be an anti-Semite. And, for that matter, when you consider that anti-semitism was endemic in Europe, the elimination of this condition would also be required. In short, the very reasons for Hitler's election and rise to power, as well as Germany's initiation of war, would need to changed in such a way that Hitler would never rise to power.
What would it take for the South to win the Civil War? I would argue that in order for the Southern states to whip the North, they would need a vast industrial base, good transportation, a well educated populace, and perhaps even a change in demeanor of whites in the South in a more curious and enthusiastic embrace of science and technology. In short, Southerners would have needed to develop the resources of the South without the use of chattel slavery. And if slavery did not exist, which perhaps would have allowed them to win, the war would never have occured.
I think you may see where I'm heading here, but if not, I'll just spell it out. The requirement to change the contingencies of history is such that the contingencies would never exist. In short, a paradox. Kurmans' Paradox (since I've found nothing in the literature which quite phrases this useless insight in the way I've described, I claim title to it). Or if you want a more time-travelly flavor:
Kurman's Law: "Any contingent change in history to alter the outcome of a turning point causes the turning point to cease to exist".