What also gets me about "what is the Nazis/the South won?" kind of stories, is that it seems to assume that if those wars had been lost, that all effective opposition stopped right there, never to regroup or be revived (until the hero from normal-time arrives, usually).
As if everybody just shrugged their shoulders and went along with it, or if there were no other path for rebellion against slavery or the Nazi regime could be found, other than the exact course of events in real history. It's extremely pessimistic.