Such as...?
Since we're talking about America's choice here, the plausible outcomes of the Lindbergh America-First strategy (rather than starting to help the Allies even before Pearl Harbor) look like a Nazi-dominated Europe, possibly including Britain, and a Japanese-ruled China. Germany-USSR was a wild card in any case, but you have to acknowledge the possibility of atrocities on even a wider scale than we saw.
Of course, World War II was almost certainly worse for the world than what would have happened if the Nazis had never tried to conquer Europe. But the choice of whether to fight seems to have been made correctly on the part of the US and UK.
Noah Millman wrote:
Link (which includes additional good retrospectives) thanks to Ampersand.
This article may have more political content than is suitable for LW-- if you'd rather discuss it elsewhere, I've linked it at my blog. I've posted about it here because it's an excellent example of updating and of recognizing motivated cognition even if well after the fact.