Personally I think the outrage is pretty premature. But the best I can tell there is at least one legitimate criticism of the concept (rather than the nonexistent execution). Essentially, the idea being that showing an alternate history where things are worse to some extent absolves the problems of the present (as opposed to a future story where things are worse, which would be a cautionary tale). Basically it’s a thing where you can point to it and say “look how much worse race relations could be, so don’t complain!”

The same criticism applies to the Man in High Castle though not sure why the outrage wasn’t there (probably a combination of a lot of different reasons).