Canonically the “D” in the acronym is understood as “doubt”, as you can see here, here (2 of 2), here. Division and infighting play no direct role here.
Uncertainty and doubt are synonymous.
They do overlap but complete synonymous are extremely rare. And I believe that, in this context, they refer to different things - the uncertainty as lack of knowledge on how something works, and the doubt on the outcome itself. (@DeltaTangoLima offers an alternate explanation, where the doubt is ideological.)